Nearly 2d electronic microparticles

ABSTRACT

An particle can include a first sheet comprising a layer including a first material, wherein the first sheet includes a first outer surface and a first inner surface; and a second sheet comprising a layer including a second material, where the second sheet includes a second outer surface and a second inner surface, wherein the first sheet and the second sheet form a space, the space is encapsulated by the first sheet and the second sheet.

CLAIM OF PRIORITY

This application is a continuation which claims priority toInternational Application No.: PCT/US2018/39876, filed Jun. 27, 2018,which claims the benefit of prior U.S. Provisional Application No.62/525,752, filed on Jun. 28, 2017, which is incorporated by referencein its entirety.

TECHNICAL FIELD

This invention relates to electronic microparticles.

BACKGROUND

Graphene and other 2D materials with atomic thickness exhibit exoticmechanical strength and flexibility and/or functional properties thathave significantly advanced numerous fields of science and technology inthe past decade. See, Novoselov, K. S. et al. Electric Field Effect inAtomically Thin Carbon Films. Science 306, 666-669,doi:10.1126/science.1102896 (2004), which is incorporated by referencein its entirety. Heterojunctions or composites (e.g. with othernanoparticles) derived from such materials can generate various micro-or nanosized functional hybrids as electronics, optoelectronics,catalysts, sensors, energy storage/generation devices amongst others.See, Liu, Y. et al. Van der Waals heterostructures and devices. NatureReviews Materials 1, 16042, doi:10.1038/natrevmats.2016.42 (2016),Novoselov, K. S., Mishchenko, A., Carvalho, A. & Castro Neto, A. H. 2Dmaterials and van der Waals heterostructures. Science 353,doi:10.1126/science.aac9439 (2016), Yin, P. T., Shah, S., Chhowalla, M.& Lee, K.-B. Design, Synthesis, and Characterization ofGraphene—Nanoparticle Hybrid Materials for Bioapplications. ChemicalReviews 115, 2483-2531, doi:10.1021/cr500537t (2015), Fiori, G. et al.Electronics based on two-dimensional materials. Nat Nano 9, 768-779,doi:10.1038/nnano.2014.207 (2014), Wang, Q. H., Kalantar-Zadeh, K., Kis,A., Coleman, J. N. & Strano, M. S. Electronics and optoelectronics oftwo-dimensional transition metal dichalcogenides. Nat Nano 7, 699-712(2012), Deng, D. et al. Catalysis with two-dimensional materials andtheir heterostructures. Nat Nano 11, 218-230, doi:10.1038/nnano.2015.340(2016), Shao, Y. et al. Graphene Based Electrochemical Sensors andBiosensors: A Review. Electroanalysis 22, 1027-1036,doi:10.1002/elan.200900571 (2010), El-Kady, M. F., Shao, Y. & Kaner, R.B. Graphene for batteries, supercapacitors and beyond. Nature ReviewsMaterials 1, 16033, doi:10.1038/natrevmats.2016.33 (2016), and Ferrari,A. C. et al. Science and technology roadmap for graphene, relatedtwo-dimensional crystals, and hybrid systems. Nanoscale 7, 4598-4810,doi:10.1039/C4NR01600A (2015), each of which is incorporated byreference in its entirety.

SUMMARY

In general, a particle can include a first sheet comprising a layerincluding a first material, wherein the first sheet includes a firstouter surface and a first inner surface; and a second sheet comprising alayer including a second material, where the second sheet includes asecond outer surface and a second inner surface, wherein the first sheetand the second sheet form a space, the space is encapsulated by thefirst sheet and the second sheet.

In certain embodiments, the first sheet further can include a secondlayer including the first material.

In certain embodiments, the second sheet can further include a secondlayer including the second material.

In certain embodiments, the first material can be graphene, molybdenumdisulfide, hexagonal boron nitride (hBN), molybdenum diselenide,tungsten disulfide, tungsten diselenide, rhenium diselenide, rheniumdisulfide, black phosphorus, platinum diselenide, tin sulfide, or tinselenide.

In certain embodiments, the second material can be graphene, molybdenumdisulfide, hexagonal boron nitride (hBN), molybdenum diselenide,tungsten disulfide, tungsten diselenide, rhenium diselenide, rheniumdisulfide, black phosphorus, platinum diselenide, tin sulfide, or tinselenide.

In certain embodiments, the first outer surface can be functionalized.

In certain embodiments, the first outer surface can be covalentlyfunctionalized.

In certain embodiments, the first outer surface can be noncovalentlyfunctionalized.

In certain embodiments, the first outer surface can be functionalizedvia π-π stacking.

In certain embodiments, the first inner surface can be functionalized.

In certain embodiments, the first outer surface can be covalentlyfunctionalized.

In certain embodiments, the first outer surface can be noncovalentlyfunctionalized.

In certain embodiments, the first outer surface can be functionalizedvia π-π stacking. In certain embodiments, the second outer surface canbe functionalized.

In certain embodiments, the first outer surface can be covalentlyfunctionalized.

In certain embodiments, the first outer surface can be noncovalentlyfunctionalized.

In certain embodiments, the first outer surface can be functionalizedvia π-π stacking.

In certain embodiments, the second inner surface can be functionalized.

In certain embodiments, the first outer surface can be covalentlyfunctionalized.

In certain embodiments, the first outer surface can be noncovalentlyfunctionalized.

In certain embodiments, the first outer surface can be functionalizedvia π-π stacking.

In certain embodiments, the first sheet can include a plurality ofnanopores.

In certain embodiments, the second sheet can include a plurality ofnanopores.

In certain embodiments, the space can include a composition.

In certain embodiments, the composition can include electronics.

In certain embodiments, the composition can include liquid.

In certain embodiments, the composition can include gel.

In certain embodiments, the composition can include a nanoparticle.

In another aspect, a method of making a particle can include preparing afirst sheet including a first substrate and a first layer comprising afirst material on a first substrate, wherein the first sheet includes afirst outer surface and a first inner surface, depositing a composition,preparing a second sheet including a second substrate and a second sheetcomprising a second material on the second substrate, wherein the secondsheet includes a second outer surface and a first inner surface,annealing the first sheet and the second sheet, and autoperforating thefirst sheet and the second sheet.

In certain embodiments, the method can further include functionalizingthe first outer surface.

In certain embodiments, the functionalizing can include covalent bonds.

In certain embodiments, the functionalizing can include non-covalentbonds.

In certain embodiments, the functionalizing can include π-π stacking.

In certain embodiments, the autoperforating can include selectivelydissolving the first substrate and the second substrate.

In certain embodiments, the autoperforating can include applyingmechanical force or heat treatment.

In certain embodiments, the first sheet can further include a secondlayer including the first material.

In certain embodiments, the second sheet can further include a secondlayer including the second material.

In certain embodiments, the composition can include electronics.

In certain embodiments, the composition can include liquid.

In certain embodiments, the composition can include gel.

In certain embodiments, the composition can include a nanoparticle.

In another aspect, a method of detecting an analyte can include applyingthe particle including a first sheet comprising a layer including afirst material, wherein the first sheet includes a first outer surfaceand a first inner surface; and a second sheet comprising a layerincluding a second material, where the second sheet includes a secondouter surface and a second inner surface, wherein the first sheet andthe second sheet form a space, the space is encapsulated by the firstsheet and the second sheet, wherein the space includes a sensor anddetecting the analyte with the sensor.

In certain embodiments, the particle can be present in a solution.

In certain embodiments, the applying the particle can includeaerosolizing the particle in a solution.

In another aspect, a device can include a sheet including a substratematerial, a power source on the substrate, a switch on the substrate anda memory element on the substrate.

In certain embodiments, the power source can be a photodetector.

In certain embodiments, the photodetector can generate voltage when itis illuminated with light.

In certain embodiments, the photodetector can include a p-nheterojunction.

In certain embodiments, the photodetector can include a monolayerincluding MoS₂ and a monolayer including WSe₂.

In certain embodiments, the switch can be a chemiresistor.

In certain embodiments, the chemiresistor can change conductance uponinteraction with an analyte.

In certain embodiments, the chemiresistor can include a monolayerincluding MoS₂.

In certain embodiments, the memory element can be a memristor.

In certain embodiments, the memristor can be turned on when a voltagefrom the power source exceeds a threshold voltage and the chemiresistordetects an analyte.

In certain embodiments, the memristor can be positioned between a firstelectrode and a second electrode.

In certain embodiments, the first electrode can include gold.

In certain embodiments, the second electrode can include silver.

In certain embodiments, the memristor can include a material includingMoS₂.

In certain embodiments, the substrate material can include a polymer

In certain embodiments, the polymer can include an epoxy polymer.

In certain embodiments, a thickness of the sheet can be no more than 5μm.

In another aspect, a method of making a device can include preparing asubstrate, depositing a first monolayer of including MoS₂ on thesubstrate, depositing a second monolayer including WSe₂ at leastpartially in contact with the monolayer including MoS₂, depositing agold electrode on a portion of the first monolayer, depositing a goldelectrode on a portion of the second monolayer, depositing a materialincluding MoS₂ in contact with the gold electrode on the first monolayerand in contact with the second monolayer, depositing a silver electrodein contact with the gold electrode, and depositing a silver electrode incontact with the material including MoS₂.

In another aspect, a method of detecting an analyte can include applyingthe device including a sheet including a substrate material, a powersource on the substrate, a switch on the substrate and a memory elementon the substrate and detecting the analyte with the device.

In certain embodiments, the device can be present in a solution.

In certain embodiments, the applying the device can include aerosolizingthe device in a solution.

Other aspects, embodiments, and features will be apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an example of syncell: two graphene sheets encapsulatenanoparticle and nearly 2D devices. FIG. 1B shows different syncellsform a functional aggregate.

FIG. 2 shows optical (left) and Raman G band map (right) of a graphenesyncell that has survived the lift-off process and recaptured on amicroscope slide.

FIG. 3 shows in-plane conductivity of graphene syncells measured as afunction of contact distances.

FIG. 4 shows vertical structure of the memory testing platform withsyncells in the middle (left), BP syncell stored in EtOH/H₂O for 1 monthstill have on/off ratio >100 and perfect memory reversibility (middle),and after each cycle the interrogated syncell is immersed in H₂O for 10mins before drying under vacuum for the next cycle of testing (right).

FIG. 5 shows multiple bit memory mapping of the syncell surface(retrieved from a free-standing water solution).

FIG. 6 shows a commercial nebulizer was used to aerosolize the syncellsand they travel through air for 30 cm before recaptured.

FIG. 7 shows statistics of syncell distribution and survival rate afterthey have been aerosolized and travelled through air.

FIG. 8 shows optical micrographs and syncell yield before and after theSBET test.

FIGS. 9A-9E show syncells to detect solution droplets. FIG. 9A showsschematic of syncells in water sprayed, collected and dried. Dropletsize <300 μm. FIGS. 9B-9C show electrical measurements and FIGS. 9D-9Eshow photoluminescence measurements before (red) and after (blue)exposure to triethylamine. Statistics in FIGS. 9C and 9E is collectedover 25 different syncells.

FIGS. 10A-10E show syncells to detect gas adsorption. FIG. 10A showsschematic of syncells incubated in saturated ammonia vapor (10 kPa) for1 h. FIGS. 10B and 10C show electrical measurements and FIGS. 10D and10E show photoluminescence measurements before (red) and after (green)exposure to ammonia. Statistics in FIGS. 10C and 10E is collected over25 different syncells.

FIGS. 11A-11G show autoperforation of graphene for microparticleconsisting of nanoparticles enclosed within graphene membrane. FIG. 11Ashows the folding dynamics (or strain deveration) when stacking a thinpolymer film (200 nm) onto a micropsot; microcylinder with an aspectratio (radius/height=100/1) was used in the finite element analysis.FIG. 11B shows one-dimensional mechanical model of a thin film with anisland under stretching force F, ε₁ and ε₂ are the strain of the filminterior and exterior to the spot and h is the height of the island.FIG. 11C shows numerical simulation of the fracture propagation of the2D sheets (e.g. graphene) with encapsulated polymer (e.g. polystyrene)spot (h=1 μm), scale bar, 100 μm. FIG. 11D shows fabrication scheme ofthe microparticles with graphene: DA1, functionalizing graphene A withM1; DA2, spin-coating poly(methyl methacrylate) (PMMA) and etching outcopper; DA3, functionalizing with M2; DB1, functionalizing graphene Bwith M3; DB2, spin-coating PMMA, etching out copper, and transferringPMMA/GB onto SiO₂/Si or PDMS; DB3, functionalizing with M4; AB4, inkjetprinting nanoparticle ink; DC1, stacking; DC2, annealing; and DC3,liftoff via dissolving PMMA layers. FIG. 11E shows the spot array beforeliftoff, scale bars, 1.0 cm and 1.0 mm. FIG. 11F shows fracture andcrack propagation of graphene layers around a single spot (t=3.7-4.8 s,scale bars, 100 μm) and multiple spots (t=6.2-9.4 s, 1000 μm) duringliftoff under microscope. FIG. 11G shows typical microparticles sampledout from the solution after liftoff, 100 μm.

FIGS. 12A-12G show characterization of the microparticles after liftoff.FIG. 12A shows mapping the 2D peak (2680 cm⁻¹) intensity ofgraphene-PS-graphene (G-PS-G) microparticle via Raman spectroscopy.FIGS. 12B and 12C are the contour profiles of G-PS-G (1 nL, 1.2 wt %ink) and G-BP (0.9 wt %)/PS-G (1 nL, 1.2 wt % ink) microparticle. FIG.12D is lateral profile curves of various micropartcles printed with 1-nLink of different concentrations and compositions. FIG. 12E shows plot ofthe diameter (d) and height of G-PS-G microparticles against the inkvolume, the inserted shows a particle with d˜34 μm, scale bar, 20 μm.FIG. 12F shows Janus particles with the broken chemistry symmetry, scalebars, 100 nm. FIG. 12G shows fluorescence images of microparticles withG/G, G/MoS₂, and MoS₂/MoS₂ surface; G is bilayer and MoS₂ is monolayer;scale bars, 100 μm.

FIGS. 13A-13H show electrical properties and memory behavior of thegraphene (bilayer) microparticles. FIG. 13A shows plot of in-planeconductivity vs. electrode distance for G-PS-G and PS control, theinserted shows the test setup. FIG. 13B shows cross-plane I-V curves ofmicroparticles G-BP (0.9 wt %)/PS-G, G-PS-G, and BP/PS. FIG. 13C showsI-V curves of three successive sweeping of 0→2→0 V (switching 1), 0→4→0V (2), and 0→6→0 V (3), and their fitting curves based on model. FIGS.13D and 13E are scanning electron microscopy (SEM) images of BP/PScomposites, and FIG. 13E is from energy selective back scattereddetector, scale bars, 1 μm. FIG. 13F shows illustration of thepercolated composite structure as a single memristor element of themicroparticle. FIG. 13G shows writing letters of “M”, “I”, “T” in a 5×3grid on a G-BP/PS-G microparticle via selective writing (0→4 V) orerasing (0→−4 V) of the grids with probe, scale bar, 100 μm. FIG. 13Hshows plot the ON/OFF ratio N at 0.2 V of G-BP/PS-G against theirstorage time in ethanol/water (1:1), each hollow symbol represents adata point measured from a random. FIG. 13H shows a plot the ON/OFFratio N at 0.2 V of G-BP/PS-G against their storage time inethanol/water (1:1), each hollow symbol represents a data point measuredfrom a random position of an individual microparticle. Standarddeviation represents an average over ˜10 microparticles.

FIGS. 14A-14D show application of G-PS-G microparticles to collect andstore environmental information and their aerosolization. FIG. 14A showsaerosolization of G-PS-G via airbrush and their collection via a boardconsisting of 21 glass slides 30 cm away. FIG. 14B shows the collectedmicroparticles (˜460) found on the board via microscope, each dotrepresents one particle and the black cycle is the spraying center. FIG.14C shows optical microscopy images of the collected microparticles withvarious folding structures and no breakage, scale bars, 200 μm. FIG. 14Dshows conceptual illustration of using two terminal electronicnano/micro-particles to collect and store the environment informationand their reading out. FIG. 14E shows a schematic illustration of thewhole operation process including information readout & write in,liftoff, recapture, and information readout. FIG. 14F shows scatteredplot of the pristine state conductance before liftoff against thepost-recapture conductance for domains with turning-on treatment andcontrol domains, data are from 4 different G-MoS₂ (0.07%)/PS-Gmicroparticles, each data point means the conductance of a specificdomain on the microparticle defined by a grid. Control points aredistributed around the diagonal line, meaning no significant conductancechange after lift off.

FIGS. 15A-15B show effect the ink composition in the inkjet-printingprocess. FIG. 15A shows mean particle size=0.5 um, 1.25 wt % in water.FIG. 15B shows mean particle size=0.5 um, 1.25 wt % in water/ethyleneglycol (50 vol. %) mixture.

FIGS. 16A-16C show effect the particle size of the PS latex nanoparticleink on the particle morphology when printing on bilayer graphene/PMMAsurface, all late particles are amine-functionalized, 1 nL, 1.25 wt % inthe mixture of ethylene glycol (1:1 vol.). FIG. 16A shows PS latex ink,mean particle size=1.0 μm. FIG. 16B shows PS latex ink, mean particlesize=0.5 μm, and FIG. 16C shows PS latex ink, mean particle size=0.1 μm.The surface of spots printed with 1.0 and 0.5 μm latex solution arenonuniform and some regions have no particle coverage, while the surfaceof spot printed with 0.1 μm latex ink are relatively uniform with a fullcoverage of PS nanoparticles.

FIGS. 17A-17G show systematical characterization of the dispersion ofblack phosphorus (BP) nanoflakes in ethylene glycol (EG). FIG. 17A showsthe well-dispersed BP nanoflakes/EG solution follows Lambert-Beer law.FIG. 17B shows Raman spectrum of the exfoliated BP nanosheets, withthree identified models of A_(g) ¹, B_(2g), A_(g) ² at ˜362, ˜439, and˜467 cm⁻¹, respectively. FIGS. 17C-17D show 2D and 3D AFM profilingimages of BP nanoflakes on Si/SiO₂ substrate, the average height isdetermined to be 0.99±0.4 nm (2±1 layers). FIGS. 17E-17F show TEM imagesof the BP nanoflakes at scale of 100 nm and 10 nm, the insert shows thefast Fourier transform (FFT) of the TEM image at the selected area. FIG.17G shows selected area (electron) diffraction pattern (SADP) of BPnanoflakes.

FIGS. 18A-18B show X-ray photoelectron spectroscopy (XPS) spectra of theexfoliated BP (FIG. 18A), P2p core-level XPS spectra of the exfoliatedBP (FIG. 18B). FIG. 18C shows the size distribution of BP nanoflakes inethylene glycol (EG) measured by Nanosight at room temperature and thestatistical mean size is 278.5±23.7 nm.

FIG. 19A shows liftoff using CHCl₃, a good solvent for both PS latexparticles and PMMA layers (FIG. 19A), no particles was found. FIG. 19Bshows liftoff with dimethylformamide (DMF) and adding waterintermediately to reduce solubility of PS in DMF, PS particles has apoor solubility in DMF/H₂O (3:1 in volume). FIG. 19C shows liftoff withEtOH/H₂O (80:20 in volume) at temperature 80° C., the solvent candissolve PMMA layer selectively while not PS, liftoff is successful.

FIG. 20A-20C show magnetic adsorption of graphene microparticles in thewater/ethanol (1:4). The particle has an interior composite fillers ofiron oxide (0.9 wt %)/PS enclosed within bilayer graphenes. Iron oxide(II,III) nanoparticles with a mean particle size of 30 nm and PS latexnanoparticles with mean particle size=100 nm was mixed in water/ethyleneglycol (1.25 wt %) for printing. Scale bars are 2.5 cm, 2.5 cm, and 0.5cm.

FIG. 21A shows nanoparticles with pristine graphene, microparticles mayhave tiny tails, using pristine CVD bilayer graphene and PS interiorfiller. FIG. 21B shows nanoparticles two sides functionalized graphene,microparticles have edges or wings, using 1-aminopyrene and1-pyrenebutyric acid N-hydroxysuccinimide ester functionalized bilayergraphene as Graphene A, and 1-pyrenebutyric acid and 1-pyrenebutyricacid N-hydroxysuccinimide ester functionalized graphene as Graphene B.Amine-functionalized PS latex nanoparticles (mean particle size=100 nm,1.2 wt % in water/ethylene glycol (1:1)) as interior filler for bothcases.

FIG. 22A shows optical microscopy image of the microparticle G-ZnO (30wt %)/PS-G with scale bar of 100 μm. FIG. 22B shows Raman mapping of its2D peak intensity at 2680 cm⁻¹ with a pixel size of 5×5 μm.

FIGS. 23A-23B shows optical microscopy images (FIG. 23A) and Ramanspectra (FIG. 23B) of G-PS-G microparticles before and after liftoff.Bilayer graphene was used in the process and the blue spots representthe position of the laser bean where the Raman spectroscopy signal wasacquired. FIG. 23C is a quantitative analysis of the intensity and the Gpeak at 1590 cm⁻¹ and 2D peak and 2685 cm⁻¹ and their ratio before andafter liftoff. Si/SiO₂ substrate was used in the fabrication. “Space”means the region at the exterior of the printed PS microspots.

FIGS. 24A-24B show Raman spectra of microparticles only having one layerof graphene (Graphene A or Graphene B only, bilayer). FIG. 24A is thefull spectra in range of 1000-3500 cm⁻¹ and FIG. 24B is the enlargedpart at 2600-2800 cm⁻¹ to show the 2D peak from graphene. Controlsamples without graphene coverage is also included for comparison.

FIG. 25 shows a statistical study of the yield of the as-prepared G-PS-Gmicroparticles fished out after liftoff, 86 microparticles of 115 aregood without breakage with a yield ˜80%. Bilayer graphene and 1 nL of PSlatex nanoparticle ink (1.2 wt % in mixture of water and ethylene glycol(1:1), mean particle size=100 nm) were used for printing, and anannealing temperature of 120° C. in the fabrication. All themicroparticles were naturally dried on glass slides after fishing outvia dropper and counted under microscopy with 5× or 20× objectives.

FIG. 26 shows a statistical study of the yield of the PS microparticlesfished out after liftoff immediately, 36 microparticles of 66 have goodshape without breakage with a yield 55%. All the fabrication operationare the same as G-PS-G in FIG. 25 except no use of graphene. All themicroparticles were naturally dried on glass slides after fishing outvia dropper and counted under microscopy with 5× or 20× objectives.

FIGS. 27A-27E show a statistical study of the yield of the G-PS-Gmicoparticles after a storage time of one week (FIG. 27A), with 18particles of 24 are good; three weeks, 24/31 (FIG. 27B); 100 weeks,39/58 (FIG. 27C); and 4 months, 34/63 (FIG. 27D). All the particles arethe same as that in FIG. 24. FIG. 27E is the study of G-ZnO (30 wt%)/PS-G microparticles after a storage time of 4 months, 24/44. All themicroparticles were naturally dried on glass slides after fishing outvia dropper and counted under microscopy with 5× or 20× objectives.

FIGS. 28A-28B show statistical study of the yield of the G-BP (0.9 wt%)/PS-G micoparticles. FIG. 28A shows fresh, 147 particles of 173 aregood, yield=85%. FIG. 28B shows after a storage time of 9 weeks, 70/92,yield=76%. All the microparticles were naturally dried on glass slidesafter fishing out via dropper and counted under microscopy with 5× or20× objectives.

FIG. 29 shows plot of the yield (or survival rate) of various graphenemicroparticles after different storage time and treatment.

FIG. 30 shows a comparison of the breakage of microparticles with orwithout graphene under microscope: (A)-(D) are the PS control particleswithout graphene coverage; (D)-(G) are G-PS-G microparticles withbilayer graphene coverage. The two particles were prepared with a sameprocedure and same PS latex ink (1 nL, 1.2 wt %, 100 nm), scale bars are200 μm.

FIGS. 31A-31D show effect of solid content of ink (0.2-1.2 wt %) on thediameters and profiles of the microparticles. FIG. 31A shows the plot ofparticle diameter, h_(peak), and h_(valley) with the solid content of PSink, FG means 1-pyrenebutyric acid N-hydroxysuccinimideester-functionalized bilayer graphene. Profile mapping and statisticaldata of particles produced with 0.2 wt % (FIG. 31B), 0.5 wt % (FIG.31C), and 0.8 wt % ink (FIG. 31D). The PS ink is 100 nm latex solution(2.5 wt %) diluted with ethylene glycol (EG) and de-ionized water to thedesired content, with an EG: water=1:1 in volume. The sample size isabout 15-20 microparticles in the statistical study of each data point.

FIGS. 32A-32D show optical microscopy images of fished microparticlesliftoff from bilayer graphene-encapsulated microspot array printed with0.25 wt % PS latex nanoparticle ink (mean particle size=100 nm, inwater/ethylene glycol (1:1) mixture), with h_(peak)=0.56±0.06 μm andh_(valley)=0.08±0.01 μm, scale bars are 800, 200, 200, and 100 μmrespectively. FIG. 32E shows Raman mapping of 2D peak signal at 2680cm⁻¹ of graphene from the particle shown in FIG. 32D.

FIGS. 33A-33B show profile results of graphene particles with innerPS/ZnO (30 wt %) (G-PS/ZnO-G) on pristine (FIG. 33A) and 1-pyrenebutyricacid N-hydroxysuccinimide ester-functionalized (FIG. 33B) graphene. FIG.33C show profile data of G-PS/BP (0.9 wt %)-G microparticles on pristinegraphene. Tables 1, 2, and 3 are the profiling results of multiplemicroparticles for statistical studies. All particles have a same inkvolume of 1 nL, 1.8 wt % ink for G-PS/ZnO-G and 1.2 wt % ink for G-PS-G.

FIG. 34A shows the printed microspot array on graphene/PMMA/PDMSsubstrate with an ink (1.25% PS latex, ˜50 nm, in mixture of water andethylene glycol (1:1)) volume of 10 pL, the scale bar is 180 um. FIG.34B-34I show optical images of G-PS-G particles after liftoff themicrospot array in FIG. 34A, the average diameter is determined to be34.2±1.4 um, all figures have the same scale bars of 40 μm. FIG. 34Jshows Raman mapping of the 2D peak from graphene on the particle shownin FIG. 34I.

FIG. 35A shows the printed microspot array on graphene/PMMA/PDMSsubstrate with an ink (1.25% PS latex, ˜50 nm, in mixture of water andethylene glycol (1:1)) volume of 1 pL, the scale bar is 140 um. FIG. 35Bshows optical microscopy images of the fished particles after liftoff,the average diameter is 18.6±2.2 um, all figures have the same scalebars of 40 μm.

FIG. 36 shows five functional molecules containing amine, carboxylicacid, —NHS groups as the candidates for M1, M2, M3, and M4. Otherfunctional pyrene or naphthalene molecules with similar structure canalso be used for the noncovalent modification of graphene via π-πstacking.

FIG. 37A shows X-ray photoelectron spectroscopy (XPS) results ofpristine bilayer graphene and 1-pyrenebutyric acid-functionalizedbilayer graphene on SiO₂/Si substrate. FIG. 37B shows the −O1s peak ofthe graphene sample can fit into a single peak, which bellows to oxygenfrom the SiO₂ substrate. FIG. 37C shows the −O1s peak of theacid-functionalized graphene can be deconvolved into three peaks, whichbelong to SiO₂, and the 2 oxygen atoms from 1-pyrenebutyric acid. FIG.37D shows water contact angle of CVD graphene and 1-pyrenebutyricacid-functionalized graphene, acid-functionalized graphene is morehydrophilic with a reduced contact angle. These results illustrate thatCVD bilayer graphene can be functionalized noncovalently via functionalpyrene molecules directly on copper substrate.

FIGS. 38A-38C show Raman spectroscopy characterization of mono- orbilayer graphenes with one side or both sides being functionalizednoncovalently (chemistry symmetry breaking). FIGS. 38A-38B show Ramanspectra of pristine monolayer graphene, bilayer graphene, and theirfunctionalized counterparts with SiO₂/Si wafer as support. FIG. 38C isdata for bilayer graphene with PMMA layer on SiO₂/Si wafer. Frompristine graphene, one-side modification, to both sides, the intensityof 2D peaks reduces while the G peak intensity increases continuously,and more small peaks attribute to —COOH or NH₂ groups emerge in range of1000-1500 cm⁻¹ and these peaks become broad and blunt when both sideswere functionalized. These demonstrate the successful introduction offunctional groups via noncovalent functionalization and the breaking ofthe chemistry symmetry.

FIGS. 39A-39B show Raman mapping of the microparticels with four-sidefunctionalized graphene, the used functional molecules are1-pyrenecarboxylic acid (exterior surface)/1-pyrenebutyric acidN-hydroxysuccinimide ester (interior surface) and 1-aminopyrene(exterior surface)/1,5-diaminonaphthalene (interior surface). FIG. 39Ais the optical image from microscope, scale bar=100 μm. FIG. 39B showsRaman mapping of the 2D peak at 2680 cm⁻¹. 1.25% wt % PS latexes(amine-functionalized, 100 nm mean particle size), 1 nL was used forprinting.

FIG. 40 shows a statistical study of the yield of functionalizedgraphene microparticles (see FIG. 39 for structure information) after astorage time of 8 months, 94 particles are good in 135, with a yield of69.6%.

FIGS. 41A-41G show characterization of monolayer MoS₂ and MoS₂—PS—MoS₂particles. FIG. 41A shows printed microspot array on SiO₂/Si substrateat scale bar of 500 and 200 μms. FIG. 41B shows optical microscopyimages of fresh MoS₂—PS—MoS₂ particles fished out from solution afterliftoff. FIG. 41C shows after a storage time of 7 days, and FIG. 41Dshows after 21 days. FIG. 41E shows Raman spectrum of monolayer MoS₂grown on SiO₂ substrate. FIG. 41F shows X-ray photoelectron spectroscopy(XPS) results of MoS₂ with various peaks from Mo and S. FIG. 41G showsXPS characterization of MoS₂—PS—MoS₂ particle (the inserted picture) andpeaks of Mo3d and S2p are identified, illustrating the coverage of MoS₂on particle surface. Raman spectroscopy study of the particles fails duethe interference of polystyrene on the characteristic peaks (E¹ _(2g)and A_(1g) peaks).

FIGS. 42A-42G show characterization of multilayer hBN and hBN-PS-hBNparticles. FIG. 42A shows printed microspot array on PDMS substrate atscale bar of 200 μm. FIG. 42B shows optical microscopy images of freshhBN-PS-hBN particles fished out from solution after liftoff, FIG. 42Cshows images of particles fished out after a storage time of 3 days, andFIG. 42D after 21 days. FIG. 42F shows Raman spectrum of multilayer hBNtransferred on Cu substrate, the peak of BN-vibration “in plane” isidentified at 1370 cm⁻¹. FIG. 42G shows X-ray photoelectron spectroscopy(XPS) results of hBN with the identified peaks of N and B. FIG. 42Hshows XPS characterization of hBN-PS-hBN particle (the insertedpicture), peaks of N1s and B1s are identified. Raman spectroscopy studyof the particles fails due the interference of PS on the characteristicpeaks of BN vibration.

FIG. 43 shows fluorescence imaging of multiple 2D Janus particles withλ_(exc)=550 nm, PL intensity is normalized by exposure time, 10×objective lens, background is subtracted, scale bars are all 250 μm.

FIG. 44 shows fluorescence imaging of multiple 2D Janus particles withλ_(exc)=550 nm, PL intensity is normalized by exposure time, 5×objective lens, background is subtracted, scale bars are all 200 μm.

FIG. 45A shows typical I-V curves in the measurement of in-planeconductivity of G-PS-G (bilayer graphene was used) microparticles inplane. FIG. 45B shows the plot of resistance against the distancebetween two electrode for various G-PS-G micropoarticles. FIG. 45C showsthe calculation of the sheet resistance of the microparticle and thecontact resistance between the two electrodes and graphene surface. Thesheet resistance data of FIG. 45B was used and the sheet resistance isdetermined to be 890±420 Ω/sq with contact resistance of 5540Ω. FIG. 45Dshows the conductivity of the G-PS-G particles reduced by ⅓ after astorage time of 4 months in ethanol/water (4:1).

FIGS. 46A-46D show the measurement and calculation of in-plane sheetresistance and contact resistance between the probe electrode and PSsurface. FIG. 46A shows the optical image of the testing setup. FIG. 46Bshows the measured I-V curve. FIGS. 46C-46D are the plots ofconductivity and resistance against electrode resistance, respectively.The same calculation method as FIG. 45 was used and the sheet resistanceis 4.3*10¹³ Ω/sq and the contact resistance is 2.5*10¹⁴Ω.

FIGS. 47A-47C shows the measured I-V curves from of three G-PS-Gmicroparticles without BP, three different cycles with a same procedure0 V→4 V→0 V→−4 V→0 V was listed for each particle. FIG. 47D shows astatistical study of the cross-plane conductivity of various G-PS-Gmicroparticles at 0.2 V.

FIGS. 48A-48C show I-V characteristics of three fresh Gr-BP/PS-Grmicroparticles. Vertical conductivity hysteresis can be observed andON/OFF ratios over 10⁴ can be found in all samples tested. Each CV scanfollows a 0V→4V→0V then 0V→−6V→0V pre-programmed procedure where alarger negative voltage (−6V) is applied to ensure a fully switched-OFFconductivity state. Each plots shows three sets of consecutive cycles,with the cycle number labeled by the data. Insets shows the opticalimage of the microparticle tested, with scale bar marking 100 μm.

FIG. 49 shows the cross-plane I-V curves of four PS microparticleswithout graphene at CV scan 0 V→4 V→0V then 0 V→−4 V→0 V.

FIG. 50A shows schematic illustration of the spreading current andequipotential line within the Gr-BP/PS-Gr vertical stack (side view).Since the BP/PS composite can use the spreading electrons and drain theapplied voltage to move the oxygen vacancies around its interiorstructure, there is a limited radius of the effective voltage, δ, beyondwhich the BP is virtually unaffected. FIG. 50B shows optical micrographof a Gr-BP/PS-Gr microparticle sandwiched in between a standard 16×16gold electrode array (256MEA30/8iR-ITO, Multichannel Systems) and an ITOglass slide. Each contacted electrode is capable of readout particlevertical conductivity. FIG. 50C shows scanning electron micrographs(top, Signal=ESB, EHT=1.50 kV, WD=5.4 mm, I probe=100 pA, Mag=9.63k,Column mode=Analytic; bottom, Signal=HE-SE2, EHT=1.00 kV, WD=5.3 mm, Iprobe=50 pA, Mag=9.63k, Column mode=Analytic) of the Gr-BP/PS-Gr crosssection. White dash illustrate a potential BP pathway formed within thevertical structure. Right figure is a schematic illustration of thisvertical stack, with black shades as graphene terminals, blue as PSnanoparticles, white as BP nanoflakes, red dash as potential pathwaysconnecting the two graphene terminals. FIG. 50D shows schematicillustration of a multiple-bit (15) memory array on top of a singleGr-BP/PS-Gr microparticle, with each bit covering an area of radius δ,the critical voltage spreading radius. Red shade refers to written-inhigh conductivity bits, and white shades refers to non-written lowconductivity points. FIG. 50E shows measured conductivities at 0.2 Vreadout voltage after written-in the letter “T” in a 15-bit map, asdesigned in part FIG. 50D. FIG. 50F shows snap shot of the probe testingvertical conductivity of each of the 15 bit for the experiment shown inFIG. 50E. All scale bars represent 200 μm except for those labeled inFIG. 50C.

FIG. 51A shows I-V characteristics of an example Gr-BP/PS-Grmicroparticle stored in ethanol/water (4:1) solution for 10 days.Vertical conductivity is measured following a 0V→4V→0V then 0V→−6V→0Vprocedure for 100 consecutive cycles (with virtually no intermittencebetween each cycle). Presented here are I-V characteristics of cycle 41through 50. Insets shows the optical image of the microparticle tested,with scale bar marking 100 μm. FIG. 51B shows measured Gr-BP/PS-Grvertical conductivity ON/OFF ratios at 0.2 V querying source-drainvoltage for 100 cycles. A slow pre-conditioning process can be found forthe first 20 cycles, a previously unidentified trait unique for this2D-material-polymer composite system, presumably due to the largevertical distance the composite covers (1 μm). The excellent ON/OFFratio maintains above 1.0×10³ from cycle 40 to cycle 80 and falls offafterwards. This could due to the worn-out graphene electrodes due torepeated CV scanning. The average ON/OFF ratio across all 100 cyclestested is marked with the red dotted line, and has a numerical value of4160.

FIGS. 52A-52C show I-V characteristics of three Gr-BP/PS-Grmicroparticles submerged in ethanol/water (4:1) solution for 20 days.Vertical conductivity hysteresis can be observed and ON/OFF ratios over10⁴ can be found in all samples tested. Each CV scan follows a 0V→4V→0Vthen 0V→−6V→0V pre-programmed procedure where a larger negative voltage(−6V) is applied to ensure a fully switched-OFF conductivity state. Eachplots shows three sets of consecutive cycles, with the cycle numberlabeled by the data. Insets shows the optical image of the microparticletested, with scale bar marking 100 μm.

FIGS. 53A-53C show I-V characteristics of three Gr-BP/PS-Grmicroparticles submerged in ethanol/water (4:1) solution for 30 days.Vertical conductivity hysteresis can be observed and ON/OFF ratios over10⁴ can be found in all samples tested. Each CV scan follows a 0V→4V→0Vthen 0V→−6V→0V pre-programmed procedure where a larger negative voltage(−6V) is applied to ensure a fully switched-OFF conductivity state. Eachplot shows three sets of consecutive cycles, with the cycle numberlabeled by the data. Insets show the optical image of the microparticletested, with scale bar marking 100 μm.

FIGS. 54A-54C show I-V characteristics of three Gr-BP/PS-Grmicroparticles submerged in ethanol/water (4:1) solution for 63 days.

FIG. 55 shows histograms of the ON/OFF ratio N values for various G-PS-G(Control-No BP) and Gr-BP/PS-Gr microparticles sampled out at differenttime periods of 0 (fresh), 10, 20, 30, and 63 days.

FIG. 56 shows the effect on the successive water treatment on the ON/OFFratio of G-BP/PS-G microparticles (20 days) for 8 cycles, for eachcycle, the interrogated microparticle was immersed in H₂O for 10 minsbefore drying under vacuum for the next cycle of testing. A 1000+ON/OFFratio (N) remains during these 8 cycles.

FIG. 57A shows X-ray photoelectron spectroscopy (XPS) spectra of freshlyprepared BP/PS, and 90-day G-BP/PS-G microparticles, no phosphoruselements retains in the last sample. FIG. 57B shows P2p core-level XPSspectra of the freshly prepared BP/PS. Note that changes in elementalcomposition with a maximum depth of about 10 nm can be documentednondestructively by XPS.

FIG. 58 shows optical microscopy images of G-PS-G microparticles withgood circular shapes after an overnight treatment in a pH=1.5 solutionof 0.4 M glycine adjusted by concentrated HCl mimicking the mammaliandigestive track, scale bars, 100 μm.

FIGS. 59A-59D shows aerosolization of the G-PS-G microparticles with anairbrush and their collection. FIG. 59A is the airbrush. FIG. 59B is thecollecting board of the microparticles. The video of the aerosolizationprocess is shown in Video? of Supplement materias. FIG. 59C is theposition distribution of all collected microparticles (˜460 particles)labeled out on the slides using optical microscope. (D) Histograms ofthe particles against distance to the spraying center.

FIG. 60 shows a statistical study of the yield of the G-PS-Gmicroparticles (same as that in FIGS. 24A-24B) after a storage time of 3weeks (77% yield via natural drying) via aerosolization. 55 particles of80 are good and the yield is 69%, scale bars, 200 μm.

FIG. 61A shows optical images and FIG. 61B shows Raman spectra of 10Gr-PS-Gr microparticles after airbrush, collected with glass slide. Bothfolded and unfolded microparticles have graphenes, scale bars, 50 μm.

FIG. 62A shows equilibrium strain field map (top view, last time step ofthe kinetic model) with adaptive non-uniform spatial grids. Insets arethe side views of this 3D simulation, with the top inset a zoom-in of asingle microspot. FIG. 62B shows equilibrium strain field of aside-viewed microspot edge, with maximum strain reaching 0.78%. FIG. 62Cshows time evolution of the relative strain as a function of radius,r=100 μm corresponds to the edge of the microspot.

FIG. 63A shows vertical profile measurement of a G-BP/PS-Gmicro-particle, with its height reaching 1 μm at the maximum towards thecenter of the particle. FIG. 63B shows schematic of the side view of amicroparticle as considered by this model, the curvature of the particleis embedded in the height h(r), and the ε₁ and ε₂ describe relativestrain for the PS/PS/graphene composite and two bilayer graphene layers,respectively.

FIG. 64A shows strain built-up due to tensile force stretching of thegraphene lattice laminated with polystyrene (PS) core. Scale bar marks100 μm, and inset shows the interior cross section of the microparticle.FIG. 64B shows relative strain of the graphene lattice and particleheight as a function of the particle radius, with the strain induced bythe initial folding and the subsequent tensile stretching adding intothe total strain.

FIG. 65A shows equivalent circuit diagram for the parallel rectifier andmemristor model. FIGS. 65B-65D show experimental (solid red) and modelfitted (black dash) for a 2 V cyclic bias voltage scan across the twoterminals of a Gr-BP/PS-Gr microparticle, with first scan (FIG. 65B),second scan (FIG. 65C), and third scan (FIG. 65D) conductedconsecutively.

FIGS. 66A-66C show syncells as a state machine. FIG. 66A shows summaryof syncell fabrication steps with side and top views schematics and topview optical micrographs: (1) SU-8 base fabrication, (2) MoS₂ and WSe₂monolayer transfer with gold evaporation forms photodetectors, (3) MoS₂flakes transfer forms memristors, while silver evaporation formselectrical contacts for MoS2 chemiresistor. Scale bars: 25 μm. FIG. 66Bshows electrical circuit diagram of syncell: the photodiode convertslight into current (generating voltage c and having the internalresistance R_(ph)), which turns on the memristor (having a thresholdvoltage V_(th) and the internal resistance R_(m)) only if thechemiresistor detected an analyte (resistance R_(ch)). FIG. 66C shows ablock diagram for the syncell state machine. The initial memory stateOFF changes to ON only in the presence of both chemical and lightsignals.

FIGS. 67A-67L show individual components of the syncell. FIG. 67A showsa diagram and FIG. 67B shows an optical picture of a syncell with aphotodetector fabricated of continuous MoS₂ monolayer and 25 μm stripedmonolayer of WSe₂. FIG. 67C shows typical current-voltagecharacteristics of a p-n photodiode composed of MoS₂ and WSe₂ monolayersunder 532 nm laser (black—in the dark, cyan, blue, green and red—under0.7, 1.75, 3.5 and 7 μW/μm² illumination intensities, respectively).FIG. 67D shows master plot for multiple devices, as in FIG. 67C. FIG.67E shows a diagram and FIG. 67F shows an optical picture of a syncellwith a chemiresistor. FIG. 67G shows several current-voltage curves fora monolayer MoS₂ chemiresistor before (red) and after the addition of 10mM TEA (blue). FIG. 67H shows master plot for multiple devices, as inFIG. 67G. The red line is a guide for the eyes. FIG. 67I shows a diagramand FIG. 67J shows an optical picture of a syncell with a memristor.FIG. 67K shows several current-voltage characteristics for a MoS₂memristor sandwiched between gold and silver electrodes. FIG. 67L showsmaster plot for multiple devices, as in FIG. 67K. In FIGS. 67D, 67H, and67L show black denotes as-fabricated devices, red—lifted off, andgreen—devices dispersed with a nebulizer. Scale bars: 25 μm.

FIGS. 68A-68F show syncell state machine operation. FIG. 68A showschemiresistor conductance changes due to syncell exposure to TEAdroplets (10 mM) during spraying, enabling memory conductance changeafter illumination with 532 nm laser 7 μW/μm². Black squares denotemeasurements before exposure and red circles—after exposure andillumination. FIG. 68B shows the same as FIG. 68A but syncells wereexposed to a carbon nanotube dispersion (0.2 g/l). FIGS. 68C and 68Dshow the same as FIGS. 68A and 68B, but for syncells on-the-substrate.Green triangles denote control measurements after illumination, bluediamonds—after exposure. FIGS. 68E and 68F show ranked memoryconductance ratio extracted from FIGS. 68C and 68D, respectively. FIG.68G shows experimental schematic demonstrating remote detection andmemory storage in a constrained environment: the leftmost nebulizerinjects CSMs (teal squares) across the enclosed tube injected witheither TEA or aerosolized carbon nanotube particulates (dark bluedroplets) using the topmost nebulizer. CSMs are collected on thecollector, exposed to light, and their memory states are queriedafterwards. FIG. 68H shows a picture of the experimental setup.

FIGS. 69A-69H show syncell (CSM) standoff detection. FIG. 69A shows CSMssprayed using a nebulizer through 10 mM TEA either 2 mg/l soot dispersedin air. Raster-scanning laser system is then used to find CSMs. FIG. 69Bshows retroreflector-CSM reflectance as the function of inclination androtational angles. The dashed line marks diffuse reflection limit2·10⁻³%. Inset shows a top view of 100 μm-retroreflectors. FIG. 69Cshows laser raster-scanning detection of 100 μm CSMs that landed afterspraying. FIG. 69D shows CSM positions extracted under a microscope:black circles—CSMs with retroreflectors on the top, red circles—CSMswith flipped retroreflectors, open circles—CSMs that were not detectedby the laser scan in FIGS. 69C and 69E. Statistics on CSMs. Schematicson the right demonstrate figure labels. FIGS. 69F-69H show same as FIGS.69C-69E, but for 30° substrate inclination angle.

FIG. 70A shows comparison between sedimentation velocity and the averageBrownian speed for particles of different sizes while in air undernormal conditions (particle density ρ=1200 kg/m³ and aspect ratioα=0.9). FIGS. 70B-70D show sedimentation speeds for particles of varioussizes, densities, and aspect ratios in air under normal conditions.

FIG. 71 shows syncell bases fabricated in different sizes and shapes.

FIG. 72A shows syncell profile scan for 1 μm thick syncells. Scale bar:50 μm. FIG. 72B shows a line scan extracted from FIG. 72A across severalsyncells. FIG. 72C shows a line scan extracted from FIG. 72A across thetop surface of a single syncell.

FIG. 73 shows syncell fabrication layout. Optical micrographsdemonstrate 100 μm square syncells. Schematics are not to scale.

FIGS. 74A-74E show types of syncell testing. FIG. 74A shows a syncell asfabricated. The inclination and rotational angle conventions aredepicted below. FIG. 74B shows after lift off and subsequent drying.FIG. 74C shows after spraying syncells in water with 7-100 m/s speedacross 0.6 m distance in air. FIGS. 74D and 74E show pictures ofexperimental tubes where syncells were sprayed. For actual experiments,these tubes were placed in fume hoods. The reference tube was used tospray syncells without any analyte, while the other tube has anothernebulizer on top that was used to introduce analytes inside the tube.

FIG. 75A shows schematics of CSM aerosolization experiment. Curvedarrows indicate CSM rotation direction. CSM experience mechanical stressand bend during: (1) propulsion inside a nebulizer and propagation inair under turbulent forces; (2) collision during landing; (3) capillaryforces during drying. FIG. 75B shows examples of 100 μm syncellsaggregating and bent during the drying process.

FIGS. 76A-76C show syncell distribution after the flight. FIG. 76A showssyncells were collected on glass slides, imaged under the microscope,and marked. Scale bar: 25 mm. FIG. 76B shows digitally-extracted syncellpositions. FIG. 76C shows distance from the center diagram extractedfrom FIG. 76B. FIG. 76D shows angle distribution diagram extracted fromFIG. 76B, showing no preferential direction.

FIGS. 77A-77C show in flight kinetics. FIG. 77A shows relaxation timedecreases with the initial speed due to high non-linear air drag. FIG.77B shows travel distance until complete stop depends on the dropletdiameter and the initial speed. FIG. 77C shows cooling time falls downwith the initial speed. FIG. 77D shows comparison between relaxationtime, cooling time (taking the initial speed to be 100 m/s), andlifetime shows that the relaxation time is much shorter as compared tothe lifetime.

FIGS. 78A-78D show monolayer MoS₂ characterization. FIG. 78A shows Ramansignature peaks. FIG. 78B shows intensity map of 406 cm⁻¹ Raman line,showing a monolayer of MoS₂ covering a syncell. FIG. 78C showsphotoluminescence. AFM mapping (FIG. 78D) and extracted profile scan(FIG. 78E) across the border of MoS₂ monolayer, showing 0.65 nm step.

FIGS. 79A-79D show monolayer WSe₂ characterization. FIG. 79A shows Ramansignature peaks. FIG. 79B shows intensity map of 252 cm⁻¹ Raman line,showing a monolayer WSe₂ patterned in 25 μm wide stripes covering asyncell. FIG. 79C shows photoluminescence. AFM mapping (FIG. 79D) andextracted profile scan (FIG. 79E) across the border of WSe₂ monolayer,showing 0.76 nm step.

FIGS. 80A-80B show optical characterization of MoS₂/WSe₂ monolayerjunction. FIG. 80A shows photoluminescence demonstrates a shift ascompared to WSe₂ photoluminescence, reflecting band gap alignmentbetween MoS₂ and WSe₂. FIG. 80B shows Raman measurements demonstrate thepresence of both MoS₂ and WSe₂.

FIGS. 81A-81F show more examples of photodetectors composed of MoS2/WSe2monolayers (black—in the dark, red—under 7 μW/μm² illumination with 532nm laser). FIG. 81G shows a typical current-voltage characteristicplotted in the linear scale. FIG. 81H shows a photocurrent generated bythe device in FIG. 81G depending on the laser illumination intensity.

FIGS. 82A-82B show triethylamine-MoS₂ binding kinetics. Change in amonolayer MoS₂ conductivity during exposure to 1 ppm of TEA (FIG. 82A)and post-exposure recovery (FIG. 82B). Red lines represent theoreticalfits.

FIGS. 83A-83E show additional memory characteristics. FIG. 83A shows atypical curve for conductance change versus voltage. FIG. 83B showssingle memristor device under several cycles. While the first cycle inall the tested devices demonstrated switching, results of further cyclesvaried. FIG. 83C shows an example of applied voltage to test a memristorshows non-uniform scan rate. FIG. 83D shows initial conductance (blackdenotes as fabricated devices, red—lifted off, and green—devicesdispersed with nebulizer). FIG. 83E shows retention test for multiplememory state.

FIGS. 84A-84C show state machine analysis for as-fabricated syncells.FIG. 84A shows chemiresistor conductance changes due to syncell exposureto triethylamine droplets (10 M), enabling memory conductance change.FIG. 84B shows syncell response from FIG. 84A for individual devices.FIG. 84C shows syncell response from FIG. 84A normalized by initialmemory conductance.

FIGS. 85A-85C show state machine analysis for as-fabricated syncells.FIG. 85A shows chemiresistor conductance changes due to syncell exposureto carbon nanotubes (0.2 g/l), enabling memory conductance change. FIG.85B shows chemiresistor ratio extracted from FIG. 85A. Upon exposure,chemiresistor ratio ranged from 43400 to 9.72·10⁶ due to non-uniformcoating of syncell surface. Prefix M stands for millions. FIG. 85C showsmemory conductance ratio extracted from FIG. 85A, showing that 16devices didn't work, while the rest changed its memory conductanceranging from 1.6 to 148.

FIG. 86A shows the particles can be collected by a conductive surfacevia aerosolization or evaporative drying, or otherwise transfer to anadhesive tape for digital information encoding, scale bars are 20 mm and1 mm. FIG. 86B shows schematic illustration of the application ofsurface-functionalized G-PS/G microparticles or their magneticcounterparts as probes to electronically sense and record chemicalspecies such as metal nanoparticles and ions in (a) water and (b) soilmatrix, these microparticles can be collected via centrifugation ormagnetic capture for electronic read out. FIG. 86C shows the surfaceconductance and FIG. 86D shows the graphene 2D peak positon of thecollected microparticles in FIG. 86B and their controls.

FIG. 87 shows Griffith length scans over all possible fracture anglesand seed crack angles from 0° to 90° (referenced to radial direction).

FIG. 88 shows A), B), and C) display 5 time elapsed states for threeindividual crack propagation events. The time evolution of the crackpath can be seen as white, and ink-jet printed microspots are displayedas yellow, where as non-supported graphene double layers (top andbottom) are colored blue.

FIG. 89 shows comparison of crack formation around a single ink-jetprinted microspot with experimental observation under opticalmicroscope. PS stands for polystyrene, Gr stands for graphene.

FIGS. 90A-90C shows Gr-PS-Gr microparticles flowing in a microfluidicchip under optical microscope. The fluid (ethanol/water, 4:1) is flowingis flowed upwards via use of a syringe pump (scale bar represents 200μm). The microparticle in FIG. 90A spins clockwise while undergoingvertical translation in the direction of the fluid flow. Themicroparticle in FIG. 90B rotates along its horizontal axis and flips onits back. Two G-PS-G microparticles in FIG. 90C travel at differenttranslational speed and collide, stick with each other, and translateforward together, forming a non-covalent link in between.

FIG. 91 shows time elapsed optical images of Gr-Fe₃O₄/PS-Grmicroparticles suspended in solution under the influence of a neodymiummagnet on the right hand side of the image. Black dots aremicroparticles. Each image is time stamped. Scale bar represents 1.0 cm.A group of microparticles were circled by white dotted line and theirtrajectories are followed as time evolves.

FIGS. 92A-92B show optical images of G-PS-G particles (same ink above)printed by capillary glass tube manually, with a printing volume about0.1-0.5 μL. The resulted particles have mm-sized diameters, a foldedstructure can be found after drying, scale bars are 1 mm for the rightfour subfigures. FIG. 92B is the Raman spectrum of the particle from theright bottom one of FIG. 92A with the identified G band and 2D peak.

FIG. 93 shows the effect of the inner functionalization of graphenesheets on the morphology of the microparticles, visible wings similar toFIG. 21B above were evidenced by the microscope images of themicroparticles, scale bar, 200 μm. The functional molecules1-pyrenecarboxylic acid and 1-aminopyrene were used for the non-covalentfunctionalization of the two interior surfaces that contact the printedPS spots, while the outer surface of the graphene layers remain pristinewithout chemical modification. 1.2 wt % PS latexes (100 nm mean particlesize, amine-functionalized) with a volume of 1 nL was used for inkjetprinting.

FIGS. 94A-94B shows typical I-V characteristics of G-GOx (1 wt %)/PS-G(FIG. 94A) and G-MoS₂ (0.07 wt %)/PS-G (FIG. 94B) microparticles at CVscan 0 V→−4 V→0 V→4 V→0 V. The insets of show the tested particles withthe left probe contacting the top surface of the microparticles, andright probe contacting the ITO/glass substrate, the whole particle isplaced on ITO/glass surface.

FIG. 95A shows illustration of the cross-plane view of multiplememristor elements with Ag spots underneath a graphene layer and thefabricated particles with silver microspot array: 1-3 are G-GOx (1 wt%)/PS-G particles, GOx/PS composite ink with solid content of 1.25 wt %and silver dispersion with a concentration about 0.15˜0.175 wt % wereused in the fabrication; 4 is G-MoS₂ (0.07 wt %)/PS-G particle, the0.625 wt % composite ink and 0.15˜0.175 wt % silver dispersion were usedfor the fabrication. Scales bars, 1 mm. FIGS. 95B-95E show typical I-Vcharacteristics of G-GOx (1 wt %)/PS-G (FIG. 95B), G-MoS₂ (1 wt %)/PS-Gmicroparticles (FIG. 95C), and G-MoS₂ (0.07 wt %)/PS-G microparticles atvarious CV scans 0 V→−4 V→0 V→4 V→0 V (FIGS. 95D-95E). The insets ofFIGS. 95C-95E show the test particles, the left probe contacting theposition of Ag spot right underneath the top graphene layer, and rightprobe contacting the ITO/glass substrate, the whole particle is placedon ITO/glass surface.

FIG. 96A shows typical I-V curve of G-MoS₂/PS-G when applying a voltagesweep from 0→5→0 V in the initial run to switch on, I and II are fromthe same microparticle but tested at different positons, III is from adifferent microparticle. The two microparticles are sampled out fromtheir dispersion in ethanol after two months of storage, scale bars, 250μm. FIG. 96B shows the captured optical images of 12 spots on a typicalmicroparticle at the stage of initial reading out (Stage I, 0-0.15 V),writing in (Stage II, 0-5 V), and the later reading out after liftoffand recapturing (Stage III, 0-0.15 V), scale bar, 250 μm. In theexperiment, after sampling and drying the microparticle onto anITO-coated glass, a grid was drawn to approximately define 12 or 8domains on the microparticle approximately to facilitate the use ofmicroprobe for reading out and writing in. The vertical resistance ofeach domain was first read out by applying a low-voltage sweeping from 0to 0.15 V without switching on the memresistive element (Stage I). Ahigh voltage sweep was subsequently applied from 0 to 5 V to switch onthe six spots labeled with red color, while keeping the other 6 spotsunchanged as control (Stage II). Ethanol solvent was further added ontothe ITO/glass slides and lift off the microparticles under mechanicalagitation. Drying the dispersion and the microparticles will sit on theITO/glass, and a voltage sweeping can be applied from 0-0.15 V to readout the vertical conductance of the 12 again (Stage III).

FIG. 97 shows results of Mann-Whitney U-tests and Wilcoxon signed ranktests (WSRT) upon conductance of control and experimental groups at eachstage (data points from FIG. 14F in the main text). Statistical analysisconfirmed an increase in conductance between Steps I and III for thecontrol group. No overall change is observed in conductance of thecontrol group. Symbols in the figure represent statistical (in)equalities between the two sets of conductance measurements.

FIG. 98A shows optical images of the collected G-GOx(1 wt %)/PS-Gparticles on copper foil tape. FIGS. 98B-98C show the I-Vcharacteristics of G-GOx(1 wt %)/PS-G particles I and II in FIG. 98A onthe conductive copper surface, respectively.

FIGS. 99A-99F show CSMs for monitoring pipeline status. FIG. 99A showsschematic of the pipe segment system (22 mm inner diameter) that usestwo separate valves for metering aerosolized CSMs (teal squares) (FIG.99A) or ammonia (FIG. 99B). To allow for retrieval, a layer ofcheesecloth served as a collector at the pipe endpoint. FIG. 99C shows apicture of the experimental setup with a crucible filled with ammonia.Once the lower valve is open, saturated ammonia vapor (˜10 kPa) expandsinto the rest of the system. FIG. 99D shows chemiresistor conductancechanges (from G_(ch) ^(in)=9.1±2.2 nS to G_(ch) ^(ƒ)=18.5±2.5 nS) due toCSM exposure to ammonia vapor, enabling a memory conductance change(from G_(m) ^(OFF)=12.5±3.9 nS to G_(m) ^(ON)=14.5±4.3 nS) afterillumination with a 532 nm laser (7 μW/μm²). Black squares and redcircles denote measurements before exposure and after exposure andillumination, respectively. FIG. 99E is same as FIG. 99D, but forcontrol CSMs on-the-substrate: Chemiresistor conductance changes fromG_(ch) ^(in)=9.5±1.3 nS to G_(ch) ^(ƒ)=18.6±2.9 nS, enabling thememristor conductance change from G_(m) ^(OFF)=11.7±3.8 nS to G_(m)^(ON)=13.7±5.0 nS, p-value equals to 0.0017. Violet triangles denotecontrol measurements after illumination, blue diamonds—after exposure.Dashed lines are guides for eyes. FIG. 99F shows ranked memoryconductance ratio extracted from FIG. 99E shows 45 CSMs successfullychange their memory conductance with an average ratio of 1.55. N=100 forall experiments.

FIGS. 100A-100D show large area sensing. FIG. 100A shows setupschematic: Soot particles are sprayed at three locations over an areawith previously dispersed with CSMs (teal squares). FIG. 100B shows apicture of the experimental setup. FIG. 100C shows digitized positionsof aerosolized CSMs. Dashed circles are guide for eyes, highlightingthree areas exposed to soot. FIG. 100D shows chemiresistor conductancechanges due to CSM exposure to soot, enabling memory conductance changesafter illumination with a 532 nm laser (7 μW/μm²).

FIGS. 101A-101C show state machine analysis for as-fabricated CSMs. FIG.101A shows chemiresistor conductance changes due to CSM exposure toammonia (˜10 kPa), enabling memory conductance change. FIG. 101B showsCSM response from FIG. 101A for individual devices. FIG. 101C shows CSMresponse from FIG. 101A normalized by initial memory conductance. Blacksquares denote measurements before exposure and red circles—afterexposure and illumination. Green triangles denote control measurementsafter illumination, blue diamonds—after exposure.

FIGS. 102A-102B show Soot characterization. FIG. 102A shows Ramanprofile under 532 nm laser excitation. FIG. 102B shows particle sizedistribution extracted from nanoparticle tracking (Nanosight LM10,Malvern).

DETAILED DESCRIPTION

Graphene and other two-dimensional (2D) materials possess desirablemechanical, electrical and chemical properties for incorporation into oronto new colloidal particles, potentially granting them uniqueelectronic functions. However, this application has not yet beenrealized because conventional top-down lithography scales poorly for theproduction of colloidal solutions. Due to its inherent stochasticity,brittle fracture is seldom used as a fabrication method for materials atthe nanometer scale. However, Griffith theory allows for the impositionof a specific strain field that can guide fracture along a pre-setdesign. Disclosed herein is autoperforation that provides a means ofspontaneous assembly for surfaces comprised of 2D molecular surfaces.Chemical vapor deposited mono- and bi-layer graphene, molybdenumdisulfide, or hexagonal boron nitride can autoperforate into circularenvelopes when sandwiching a microprinted polymer or its composite spotof nanoparticle ink, allowing lift-off into solution and thesimultaneous assembly. The resulting colloidal microparticles have twoindependently addressable, external Janus faces that can function as anintraparticle array of parallel, two-terminal electronic devices. As anexample, a 0.9 wt % black phosphorous or 0.07 wt % MoS₂nanoflake-in-polystyrene ink is printed into mono-layer graphenesandwich particles, resulting in micro-particles possessingnon-volatile, 15-bit memory storage via a spatially addressablememristor array throughout the particle interior. Such particles formthe basis of particulate electronic devices capable of collecting andstoring information in their environment. The 2D envelopes demonstrateremarkable chemical and mechanical stability for longer than four monthsof operation in aqueous buffer or even the highly acidic Humangastrointestinal environment at pH 1.5. Such particulate devices surviveaerosolization and recollection for electronic interrogation. They canalso possess specific surface chemical functionalities as capture sitesto react with particular impurity metals and ions in water samples andsoil matrices, respectively, and the ability to be recovered forelectrical readout. Autoperforation of 2D materials into such envelopestructures allows precise compositing of colloidal particulate deviceswith exotic functions, extending nanoelectronics into previouslyinaccessible environments.

Disclosed herein are a versatile colloidal micro-particle and itsfabrication technique that integrates fully extended 2-dimensionalmaterials into functional electronic circuits. These are used in thecontext of electronic state-machines, specifically water resistantmulti-bit reversible non-volatile random access memory (RAM) devices,and aerosolizable electronics that functions as a stand-alone micrometersized unit, and is capable of withstanding extreme conditions and harshenvironments.

The particles can be used to measure and track things in a specificenvironment, for example, in the human body. The particles can actcollectively. The particles can be constructed in a way to allow theparticles or a collection of particles to respond to and collect near asignaling particle that finds an event, for example, a targeted event.An analogy is the human immune system where an infection causes amacrophage to signal to other macrophages who are recruited to the siteto heal an infection. In this example, these 2D particles could form thebasis of self healing systems where damage in a material is detected byone particle that then promotes the recruitment of others to the site ofdamage to start a healing process at the damage site. Other modes caninclude cellular materials, which are materials that can mimic thefunction of human tissue and its cellular nature. Materials that consistof semi-autonomous cells can transmit information by repeating thesignal in each constituent cell, similar to the human nervous system.These particles can also store and use energy locally, avoiding theproblems of fuel diffusion through the media leading to a loss of powerdensity. In one example, human muscle tissue both stores and uses fuelin the form of glycogen using the property of a material made up ofmultifunctional cells. This type of energy storage can be utilized inthe particles described herein.

An article can include a first sheet comprising a layer including afirst material, wherein the first sheet includes a first outer surfaceand a first inner surface; and a second sheet comprising a layerincluding a second material, where the second sheet includes a secondouter surface and a second inner surface, wherein the first sheet andthe second sheet form a space, the space is encapsulated by the firstsheet and the second sheet. Each surface is functionalized individually.Certain molecules can enter syncell through nanopores (FIG. 1A).

A method of making an particle can include preparing a first sheetincluding a first substrate and a first layer comprising a firstmaterial on a first substrate, wherein the first sheet includes a firstouter surface and a first inner surface, depositing a composition,preparing a second sheet including a second substrate and a second sheetcomprising a second material on the second substrate, wherein the secondsheet includes a second outer surface and a first inner surface,annealing the first sheet and the second sheet, and autoperforating thefirst sheet and the second sheet.

A method of detecting an analyte can include applying the particleincluding a first sheet comprising a layer including a first material,wherein the first sheet includes a first outer surface and a first innersurface; and a second sheet comprising a layer including a secondmaterial, where the second sheet includes a second outer surface and asecond inner surface, wherein the first sheet and the second sheet forma space, the space is encapsulated by the first sheet and the secondsheet, wherein the space includes a sensor and detecting the analytewith the sensor. A method of making a device can include preparing asubstrate, depositing a first monolayer of including MoS₂ on thesubstrate, depositing a second monolayer including WSe₂ at leastpartially in contact with the monolayer including MoS₂, depositing agold electrode on a portion of the first monolayer, depositing a goldelectrode on a portion of the second monolayer, depositing a materialincluding MoS₂ in contact with the gold electrode on the first monolayerand in contact with the second monolayer, depositing a silver electrodein contact with the gold electrode, and depositing a silver electrode incontact with the material including MoS₂.

A method of detecting an analyte can include applying the deviceincluding a sheet including a substrate material, a power source on thesubstrate, a switch on the substrate and a memory element on thesubstrate and detecting the analyte with the device.

Microrobots can penetrate inaccessible places and perform various taskswhile remaining literally invisible. Furthermore, microrobots canpossibly assemble into bigger robots, perform a task and then scatteraway. To date, University of Michigan holds a record of miniaturizationwith millimeter-sized robots. Further reducing size of microrobots isassociated with ineffective power supplies and electronics. To overcomethis challenge, the synergy between nanotechnology and 2D electronics isused.

As used herein, the term “syncell” is a sub-millimeter programmablestate machine, where each syncell is comprised of two sheets withencapsulated 2D electronics, liquid, gel and nanoparticles. The twosheets can be graphene or another 2D layered material. The syncelloperates like a synthetic cell, with the ability to hold materials or apayload in an internal cavity between the two sheet layers. The bulgedshape is nearly 2D, with an aspect ration of a long dimension to anarrow dimension of at least about 2, at least about 5, at least about10, or at least about 100. The dimensions of the syncell can benanoscale, with the average particle size being about 10 nm, 12 nm, 15nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, or 95 nm. For other applications,syncells can have an average particle size of greater than 100 nm, forexample, less than 250 nm, less than 200 nm, or between 100 nm and 200nm. While 2D electronics dramatically reduces size of the syncell, theconfiguration has further advantages. Firstly, 2D materials can serve asmolecular barriers, which define fluid and gel regions separated fromthe surrounding solution, in very close analogy to a living cell.Secondly, nanopores present in graphene can be used to control masstransport between the interior and exterior of the syncell. Mediated by2D electronics, syncell nanopores can serve as switches, energy sourcesor even as detectors of external species. Thirdly, nanoparticleencapsulation extends any advantages of nanoparticles to the syncell.Fourthly, each of four surfaces of two graphene sheets can befunctionalized individually. Such broken symmetry particles remainchallenging to fabricate with current nanoparticle synthesis. Finally,syncell's broken symmetry is further favorable for creating functionalaggregates.

The syncells can be prepare from graphene, transition metal sulfides, orother sheet-like materials that can be fabricated into thin and flatplates.

Graphene itself, with high electron-density in its sp²-bonded aromaticrings, is impermeable to all molecules except for protons, making it thethinnest membrane for liquid/biological sample encapsulation (even invacuum conditions) and the ideal protective barrier against harshenvironments. See, Bunch, J. S. et al. Impermeable Atomic Membranes fromGraphene Sheets. Nano Letters 8, 2458-2462 (2008), Hu, S. et al. Protontransport through one-atom-thick crystals. Nature 516, 227-230,doi:10.1038/nature14015 (2014), Mohanty, N., Fahrenholtz, M., Nagaraja,A., Boyle, D. & Berry, V. Impermeable Graphenic Encasement of Bacteria.Nano Letters 11, 1270-1275, doi:10.1021/n1104292k (2011), Yuk, J. M. etal. High-Resolution EM of Colloidal Nanocrystal Growth Using GrapheneLiquid Cells. Science 336, 61-64, doi:10.1126/science.1217654 (2012),and Prasai, D., Tuberquia, J. C., Harl, R. R., Jennings, G. K. &Bolotin, K. I. Graphene: Corrosion-Inhibiting Coating. ACS Nano 6,1102-1108, doi:10.1021/nn203507y (2012), each of which is incorporatedby reference in its entirety. Meanwhile, introducing nanopores ontographene membranes allows transport of biomolecules, salts and waterwith high selectivity. See, Schneider, G. F. et al. DNA Translocationthrough Graphene Nanopores. Nano Letters 10, 3163-3167 (2010), Garaj,S., Liu, S., Golovchenko, J. A. & Branton, D. Molecule-hugging graphenenanopores. Proceedings of the National Academy of Sciences 110,12192-12196 (2013), Surwade, S. P. et al. Water desalination usingnanoporous single-layer graphene. Nat Nano 10, 459-464,doi:10.1038/nnano.2015.37 (2015), Celebi, K. et al. Ultimate PermeationAcross Atomically Thin Porous Graphene. Science 344, 289-292,doi:10.1126/science.1249097 (2014), and Cohen-Tanugi, D. & Grossman, J.C. Water Desalination across Nanoporous Graphene. Nano Letters 12,3602-3608, doi:10.1021/n13012853 (2012), each of which is incorporatedby reference in its entirety. Analogously, the smallest unit oflife—cell, consisting of cytoplasm enclosed within a thin plasmamembrane, can perform various functions like transport of molecules,chemical reactions (i.e. metabolism), locomotion, and reproduction.Graphene can be used as a membrane material to encapsulate small-sizedfunctional devices, just like those organelles in a biological cell, andby taking advantage of recent advances in 2D materials, to generateprototype “synthetic cells” (SynCell) that can flow freely in solutionand perform simple functions. Note that nano or microsized SynCells orstate-machines that can perform very simple tasks such as computing,data storing, sensing, and actuation can be interconnected into complexnanonetworks for novel applications in environmental, biomedical, andmilitary technologies. See, Akyildiz, I. F., Jornet, J. M. & Pierobon,M. Nanonetworks: a new frontier in communications. Commun. ACM 54,84-89, doi:10.1145/2018396.2018417 (2011), and Akyildiz, I. F.,Brunetti, F. & Blázquez, C. Nanonetworks: A new communication paradigm.Computer Networks 52, 2260-2279 (2008), each of which is incorporated byreference in its entirety. Herein, the controlled fracturing (termed“autoperforation”) of 2D materials as a scalable fabrication techniquefor free-flowing microparticles that function as two-terminal electronicdevices with multiple embedded memristor elements (FIG. 14D). See,Strukov, D. B., Snider, G. S., Stewart, D. R. & Williams, R. S. Themissing memristor found. Nature 453, 80-83 (2008), and Tour, J. M. & He,T. Electronics: The fourth element. Nature 453, 42-43 (2008), each ofwhich is incorporated by reference in its entirety. These microparticlesare stable in aqueous environments, in the mammalian digestive track,and can even survive the turbulent nebulization process inside aerosoldroplets. Upon collection onto a conductive indium tin oxide (ITO)surface, each memristor element can be electrically addressed and itsbipolar resistance switching behavior can be used as a multi-bitreversible random access memory (RRAM) device.

Recent studies suggests that the classic Griffith criterion of brittlefracture remains valid for graphene. See, Zhang, P. et al. Fracturetoughness of graphene. Nature Communications 5, 3782 (2014), and Yin, H.et al. Griffith Criterion for Brittle Fracture in Graphene. Nano Letters15, 1918-1924, doi:10.1021/n15047686 (2015), each of which isincorporated by reference in its entirety. A crack propagates while newcrack surfaces generate to release the elastic energy. See, Griffith, A.A. The Phenomena of Rupture and Flow in Solids. PhilosophicalTransactions of the Royal Society of London. Series A, Containing Papersof a Mathematical or Physical Character 221, 163-198 (1921), which isincorporated by reference in its entirety. A characteristic lengthscale, known as the Griffith length (L), defined as the ratio of thesurface energy (γ) to the elastic energy (Eε², where E is the elasticmodulus and ε the strain). A crack will not grow when its size is lessthan L. Large-area graphene or other 2D materials prepared by thechemical vapor deposition (CVD) method (see, Reina, A. et al. LargeArea, Few-Layer Graphene Films on Arbitrary Substrates by Chemical VaporDeposition. Nano Letters 9, 30-35 (2009), Kim, K. S. et al. Large-scalepattern growth of graphene films for stretchable transparent electrodes.Nature 457, 706-710 (2009), and Li, X. et al. Large-Area Synthesis ofHigh-Quality and Uniform Graphene Films on Copper Foils. Science 324,1312-1314 (2009), each of which is incorporated by reference in itsentirety, albeit mechanically robust (see, Lee, G.-H. et al.High-Strength Chemical-Vapor-Deposited Graphene and Grain Boundaries.Science 340, 1073-1076 (2013), which is incorporated by reference in itsentirety), usually carries intrinsic nanometer-sized defects originatedfrom the CVD and subsequent transfer processes, and these seed crackformation is stochastic in nature. In the Griffith formulation, Ldepends on ε, thereby allowing us to regulate the strain field on thegraphene or other 2D surfaces, and manipulate the fracture trajectoryfor device fabrication. Placing isolated stiff islands (e.g.semiconductor devices) on top of an otherwise compliant substrate, suchas a polymer film, can create a strain field that reduces the tensionbuilt-in the substrates covered by the those islands. See, Hsu, P. I. etal. Spherical deformation of compliant substrates with semiconductordevice islands. Journal of Applied Physics 95, 705-712 (2004), and Sun,J.-Y. et al. Debonding and fracture of ceramic islands on polymersubstrates. Journal of Applied Physics 111, 013517 (2012), each of whichis incorporated by reference in its entirety. A more recent study showsthat conforming a flat elastic sheet to a rigid substrate with Gaussiancurvature can control the sheet crack growth upon stretching. See,Mitchell, N. P., Koning, V., Vitelli, V. & Irvine, W. T. M. Fracture insheets draped on curved surfaces. Nat Mater 16, 89-93 (2017), which isincorporated by reference in its entirety.

An active area of exploration for constrained environment sensing isexternal imaging, including ultrasound for geological exploration andhuman body applications, thermal imaging for chemical reactors and gasleak detection, magnetic resonance to probe the human body and porousmaterial beds. Such imaging methods are necessarily indirect and limitedin their penetration depth. Inaccessibility often results from systemswhere the scaling of sensor networks is highly unfavorable, such aspipelines or geological targets. For other systems, direct methods areavailable, such as endoscopes and borescopes, while the problem of oilwell monitoring has benefited from fiber optic cabling for temperatureand other measurements, but such approaches are typically limited tomajor pathways and arteries of accessibility. See Mooney, W. D. &Brocher, T. M. Coincident seismic reflection/refraction studies of thecontinental lithosphere: A global review. Reviews of Geophysics 25,723-742 (1987), Frøkjær, J. B., Drewes, A. M. & Gregersen, H. Imaging ofthe gastrointestinal tract-novel technologies. World Journal ofGastroenterology: WJG 15, 160-168 (2009), Jarenwattananon, N. N. et al.Thermal maps of gases in heterogeneous reactions. Nature 502, 537(2013), Murvay, P.-S. & Silea, I. A survey on gas leak detection andlocalization techniques. Journal of Loss Prevention in the ProcessIndustries 25, 966-973 (2012), Amitay-Rosen, T., Cortis, A. & Berkowitz,B. Magnetic Resonance Imaging and Quantitative Analysis of ParticleDeposition in Porous Media. Environmental Science & Technology 39,7208-7216 (2005), Hara, A. K., Leighton, J. A., Sharma, V. K., Heigh, R.I. & Fleischer, D. E. Imaging of Small Bowel Disease: Comparison ofCapsule Endoscopy, Standard Endoscopy, Barium Examination, and CT.RadioGraphics 25, 697-711 (2005), Inaudi, D. & Glisic, B. Long-RangePipeline Monitoring by Distributed Fiber Optic Sensing. 763-772 (2006),Kurniawan, N. & Keuchel, M. Flexible Gastro-intestinalEndoscopy—Clinical Challenges and Technical Achievements. Computationaland Structural Biotechnology Journal 15, 168-179 (2017), andGalappaththi, U. I. K., De Silva, A. K. M., Macdonald, M. & Adewale, 0.R. Review of inspection and quality control techniques for compositewind turbine blades. Insight—Non-Destructive Testing and ConditionMonitoring 54, 82-85 (2012), each of which is incorporated by referencein its entirety.

Graphene Syncell as a Stand-Alone Water Resistant Multi-Bit Non-VolatileRandom Access Memory (RAM) Device

Due to the fabrication process, the syncell top and bottom graphenelayers can be electronically insulated, which provides an ideal verticalstructure of a duo-electrode system where graphene sheets are used asthe two electrical terminals. It should be noted that the coverage ofgraphene over the syncell surface is perfect, as characterized usingRaman spectroscopy of the lifted-off syncells (FIG. 2).

The in-plane conductivity of these colloidal particles was explored andan in-plane sheet resistance was 2×10⁻⁴ times that of the polystyrenecontrol without the graphene top and bottom layer. This sheet resistanceincreased 1.5 times after storing the syncells 4 months in solution(water/ethanol mixture) (FIG. 3). The actually material sheet resistanceis extrapolated from the slope.

By placing liquid exfoliated black phosphorus (BP) nano-flakes withinthe interior of the graphene cell (FIG. 4, left), reversiblenon-volatile memory was observed upon voltage stimulation, as seen inthe current-voltage hysteresis behavior (FIG. 4, middle). This on/offratio of the syncell vertical conductivity can reach 10,000 for asyncell that has been stored in solution for 10 days. Pro-longed storageof the device in water up to a month showed decreased on/off ratio(˜100), but it still remains functional (FIG. 4, middle). The samedevice gives similar on/off ratios even after been put under water for10 minutes in between cycles for up to 8 cycles (FIG. 4, right).

Due to the limited range of the spreading current on the syncellsurface, multiple bit can be addressed separately over the entiresyncell surface (FIG. 5). The letters “M”, “I”, “T” were purposefullywritten in and read out on the same syncell surface with an on/off ratioover 100. Each point is treated 0 V or −6 V (depending whether it issupposed to be on or off) before conductivity interrogation at 500 mV.The surveyed area shows reliable activity (on/off>100). The letter “M”,“I”, “T” are written in sequential order and the memory effect isaddressed point by point 5 mins after it is written.

Mechanical and Chemical Stability of Graphene Syncells

Mechanical Stability as Syncells Travel Through Air Like Aerosols

Syncells are capable of surviving highly turbulent area travel afterbeen nebulized from a water solution and sprayed across a 30 cm distancein air with an air brush (FIG. 6, left). The syncells are thenintercepted in air with 21 microscope slides where they are beingcounted under optical microscope (FIG. 6, middle). Here each dotrepresents a position of a micro-meter sized syncell that are fullyintact. Then the photograph was image processed and detailed locationprofile using MATLAB was generated (FIG. 6, right).

The statistics of the syncells survived air travel was plotted as afunction of distance to center where the nebulizer points (FIG. 7,left). The linear dependence of # of syncells as a function of theirdistance to center of spray signify even distribution of syncells. Thesyncells demonstrate excellent stability as they travel through air inthe form of aerosolized particles (69% syncell yield) (FIG. 7, right).

i. Chemical Stability as Syncells Travel Through Mammalian DigestiveTrack (In Vitro Results Using Stomach Acid Model Solution)

The mammalian digestive track corrosive environment was mimicked to testsyncell stability, an in vitro protocol that was widely used wasborrowed as the test environment: SBET (Simple BioaccessibilityExtraction Test): 100±0.5 mL extraction fluid (0.4 M glycine adjusted topH 1.5 with concentrated HCl) is added to 1.0±0.5 g of dry weight ofthings to be digested. This mixture is rotated end-over-end at 37 C at30±2 rpm for 1 h. It should be noted that syncells subjected to thistest suffers no loss in integrity (FIG. 8). There is no morphologicaldifference in cell structure before and after the in vitro test (notethe crystals in the micrograph after treatment is residual glycine).

MoS₂ Syncell as Aerosolizable Electronics, Specifically Used as ChemicalSensors

Microrobots are not so small, mainly because of power limitations.However, even with basic capabilities, new capabilities of simplechemiresistors can sense analytes over big volumes. Moreover, using 2Dmaterials dramatically reduces size and weight of such devices, makingthem actually freely flow in air.

Here, aerosolizable electronic microparticles are capable of detectinganalytes in air with subsequent to access to the detection event throughelectronic readout. This will be the first micrometer particleincorporating electrical contact on its surface. In certain embodiment,a microparticle can consist of polymer base, golden contacts andmonolayer MoS₂ acting as a sensor.

Design

Fog droplets are in the range of 10-100 um, while rain droplets arebigger. Similar design rules apply to the particles: simple calculationson drag show that particles need to be smaller than 100 um tosuccessfully float in air.

While many nanoparticles and microparticles exist that can senseanalytes in air, the condition of post-electrical readout puts newconstrains. Normally electrical circuits are designed on planarinterfaces and only recently starting on bended flexible ones. Thedifficulty of fabricating a particle with electrical contacts isassociated with the careful choice materials and their respectivedevelopers that often have to be orthogonal, meaning that independentphotolithography steps can be performed. All fabrication steps shouldnot dissolve substrate, but eventually syncell should be lifted off.

MoS₂ Sensing

MoS₂ monolayers are changing their properties when analytes adsorb ontheir surface. This happens because of electron or holes MoS₂ doping,depending on the analyte type. Change in carrier concentration affectsMoS₂ conductivity σ:σ=e×n×μ, where e is electron charge, n carrierconcentration and μ electron mobility. Number of carrier also modifiesnon-radiative decay time, affecting MoS₂ photoluminescence. Indeed, MoS₂photoluminescence is caused by radiative decay of photoexcited excitons.Modification of non-radiative lifetime leads to photoluminescencemodification and peak spectral shift.

To demonstrate MoS₂ sensing capabilities, triethylamine droplets weredispersed on the way of aerosolized syncells (FIG. 9A). FIG. 9A showsschematic of syncells in water sprayed at 150-400 m/s speed across 0.3 mdistance of dispersed triethylamine droplets (10 M), collected and driedfor 1 h. Droplet size <300 μm. Syncells were collected after 0.3 m longflight in the air, dried and subsequently their optical and electricalproperties measured. Change in conductivity was about 36 nS (FIGS. 9Band 9C), while photoluminescence was quenched and red shifted till about685 nm (FIGS. 9D and 9E).

Similarly, gas detection was demonstrated on example of ammoniadetection (FIG. 10A). After 1 h exposure to the saturated vapor ammoniavapor pressure (10 kPa), MoS₂ resistance increases to about 29 nS (FIGS.10B and 10C) and photoluminescence quenches, redshifting its peakposition to about 682 nm (FIGS. 10D and 10E). When aerosolized, syncellsinitially travel inside the solvent droplet, which eventually dries out.Drying time is usually faster than gas diffusion into the droplet.Therefore, gas adsorption onto dried syncells is usually a case. Gasadsorption is a slow process; therefore, gas either spread over bigvolume or have high concentration for flying syncell to detect it.Alternatively, syncell sedimentation speed is very slow and can prolongsyncell interaction time with the gas.

The particles described herein can be made using alternative syntheticroutes. For example, synthetic cells can be produced from 2D materialfracture and self assembly or by top-down lithography. There are othermethods that can be used as well. For example, the synthesis of selfassembling Janus particles that have different functions incorporated ina radially asymmetric way can form larger clusters with pre-designedfunctions within. Also, a heirarchy of cellular particles can be used tobuild up more complex particles from them. This can include placingsmaller cells within a larger cell to isolate certain functions.Biological cells do this in the formation of organelles that havespecific functions. Smaller 2D material cells that serve the function ofmemory, energy, sensing, light detection, communications, reproductionand repair (and not limited to this list) could be combined andincorporated into larger particles to serve specific tasks.

Autoperforation of Graphene for Free-Flowing 2D ElectronicMicroparticles with Memory

Due to its inherent stochasticity, brittle fracture is seldom used infabrication. Herein, fracture in 2D materials can be templated andguided by encapsulating particles that create a local strain field. Forpolymer-supported chemical vapor deposited graphene, molybdenumdisulfide, hexagonal boron nitride (hBN), molybdenum diselenide,tungsten disulfide, tungsten diselenide, rhenium diselenide, rheniumdisulfide, black phosphorus, platinum diselenide, tin sulfide, or tinselenide, when sandwiching an printed microspot array and lifted-offinto solution, fracture-driven perforation, or “autoperforation”, of 2Dsheets occurs along the edges of each spot. This generates colloidalmicroparticles with well-defined 2D surface layers and controllablesurface functionalities on either side. Graphene-based particlesfunction as free-flowing electronic devices with complex functionality.For example, printing a mixed ink of polystyrene (PS) nanoparticles andblack phosphorous (BP) nanoflakes yields a percolated BP (0.9 wt %)/PScomposite spot and turns each particle into a two-terminal memristorarray with time-dependent electrical memory. These particles exhibitextraordinary chemical-resistivity and mechanical stability duringmonths of preservation in an aqueous environment, overnightgastrointestinal test, and aerosolization. Autoperforation of the 2Dmaterials, in this way, opens the door to precise compositing of 2Dmaterials with various micro- and nano-objects for functionmanipulation/generation.

Disclosed herein is an “autoperforation” method that exploits the strainfield induced by the encapsulated materials to guide crack propagationwithin CVD-grown 2D films, and prepare microparticles consisting offunctional nanoparticles sandwiched in between two graphene membranes(FIGS. 11B-11H). Specifically, two copper-supported graphene sheets(monolayer or bilayer) graphene A and B, after a series of manipulations(including functionalization (optional), spin-coating of poly(methylmethacrylate) (PMMA) layer, copper etching, and inkjet printing), arestacked, encapsulating a printed microspot array, to form a sandwichedstructure on a PDMS or SiO₂/Si substrate (FIG. 11B). For the inkjetprinting, 1 nL ink of polystyrene (PS) latex nanoparticle solution (1.2wt %, mean particles size=50 or 100 nm, see ink composition and particlesize effect in FIGS. 15A-15B and 16A-16C) or its composites with othernanoparticles like 30 wt % ZnO (8-16 nm size), 1.9 wt % iron oxide(II,III) (30 nm), or 0.9 wt % black phosphorous (BP) (liquid-exfoliated, 1-3layers, ˜280 nm size, see characterization data in FIGS. 17A-17G and18A-18B) was used. After stacking, drying at ambient temperature inducescapillary forces that can promote the folding/attaching of graphene Aonto the array. Further annealing at 120° C. softens PMMA layer andenhances the binding between two graphene layers and their interactionwith the microspots. Lifting off the sandwiched structure by selectivelydissolving the PMMA layer in EtOH/H₂O (4:1) at 80° C. (a case ofsolvency (see, Polymer Hand Book, 2nd ed.; Brandrup, J., Immergut, E.H., Eds.; John Wiley & Sons: New York, Chapter IV, p-244, which isincorporated by reference in its entirety), see solvent effect in FIGS.19A-19C) “hatches” all the microspots from the substrate into thesolution (FIGS. 20A-20C). The microspot array guides the crack path ofgraphene sheets along the spot edges during this liftoff (FIGS. 11E and11F), and this process was termed as “autoperforation”. Magneticagitation accelerates autoperforation and “cutting out” pancake-shapedmicroparticles with diameters 260 μm and some of them may have tails(FIGS. 11A-11G and 21A-21B). They are essentially graphene laminatedcolloid particles that can freely rotate, flow, and interact with eachother in solution. Not only can their locomotion be manipulated bytuning the laminar flow patterns, embedding iron oxide nanoparticlesinside enables magnetic propulsion. They can be sampled together withsolvents and dried on glass slides for further characterization.

For example, an addition to the particles that could grant themlocomotion is putting Pt on one side in such a way that they will movein a H₂O₂ bath by decomposition of this molecule to O₂ and H₂O. The useof glucose oxidase near the Pt could result in the same locomotion withglucose in the medium instead of H₂O₂, since glucose reacts at thisenzyme to the lactone, yielding H₂O₂ which then can decompose. Thisability to use a chemical bath to power the particle and give it theability to move solves the problem of finite energy storage inside ofthe particle itself. One can also design a ‘governor’ in the form of ahydrogel that is porous, which can swell and contract in response tosome input stimulus. Temperature, pH and specific chemical binding canall be used to dynamically control this swelling. If the Pt catalyst isplaced on the other side of this hydrogel, separated from the solution,then the reaction and the resulting impulse for motion can be slowed oraccelerated by the contracting or expanding of the hydrogel,respectively. This can allow functions within the particle such asdetection and memory to control motion, via stimuli to the hydrogel suchas temperature, pH, chemical binding etc. A particle that releases acid,for example, can influence this governor and control motion. Thisrelease can also stimulate other nearby moving particles, causing themto move or stop collectively, hence mimicking aspects of the humanimmune system where signaling, recruitment and locomotion are controlledfor a collection of actors.

In another example, 2D materials can be implemented as atomically-thinmolecular barriers. These barriers can encapsulate analytes insidemicroparticle with an ability of releasing analytes through pores in 2Dmaterials. Additionally, these pores can allow flux of analytes insidemicroparticles. Such liquid and gas exchange can also take place insidethe microparticle, where 2D materials form isolated volumes, similarlyto cells' organelles.

In certain embodiments, outer surface can have patterned electroniclayouts. The interaction of several microparticles with such layouts canshortcut electrical connection, altering electronic layout and changingparticle functions and capabilities. Microparticle function is thereforedetermined by the presence of other microparticles. Differentmicroparticles can induce different circuits on top of the microparticleupon their contact.

The microparticle has well-preserved graphene on both surfaces and thegraphene sheet significantly improves the colloidal stability during theliftoff and storage (FIGS. 11H and 11I). Raman mapping the 2D peaksignal at 2680 cm⁻¹ of the graphene-PS-graphene (G-PS-G) microparticleconfirms the complete coverage of bilayer graphene on its surface (FIG.11H and G-ZnO/PS-G in FIGS. 22A-22B). Little change occurs to thegraphene G and 2D peak intensity as well as their ratios before andafter liftoff (FIGS. 23A-23B). Only one layer of graphene (eithergraphene A or B) can be introduced on to the particle viaautoperforation (see Raman spectra results in FIGS. 24A-24B). To studythe stability (measured in “yield”, or survival rate) of themicroparticles in ethanol/water (1:1) over time, particles were sampledout with a number up to 170 at different storage time and documented thepercentage with no visible physical damage, i.e., in good circular shape(see microscopy images of all particles in FIGS. 25-29). G-PS-G has ayield of 0.80 after liftoff, substantially higher than 0.55 for controlparticles without any graphene protection (FIG. 34I). This yield slowlydecreases with time and goes down linearly to 0.54 after 4 months.Compositing PS with BP nanoflakes increases the yield appreciably,reaching 0.85 at the beginning and 0.76 after 9 weeks of the aqueousstorage (FIG. 34I). Note that the fracture modes of graphenemicroparticles are different from the controls, with graphene ones morelikely to break via tearing while controls typically smash to tinyfragments quickly from the center (FIG. 30).

The lateral profiles of microparticles were measured (FIGS. 12A-12C) andthe geometry data were combined with modeling (FIGS. 12D-12F) tounderstand the above process. G-PS-G microparticle approximates aconcave toroid (FIG. 12A) with average peak height (h_(peak)) of 1.1 μmand valley height (h_(valley)) of 0.4 μm, affording the observed“M-shaped” profile (FIG. 12C). Lowering ink concentration to 0.2 wt %can linearly reduce h_(peak) to 0.6 μm, h_(valley) 0.1 μm, and thediameter about 160 μm (FIGS. 12C and 31A-31D). Compositing PS with BP orZnO nanoparticles will alter the particle to a convex dome (FIG. 12C)with a similar diameter ˜260 μm and tunable h_(peaks) between 0.8 and1.2 μm (FIGS. 12C and 32A-32D).

A coarse grained finite element model was first constructed to visualizethe folding dynamics of a PMMA/graphene film onto the printed microspots(regular microcylinders with an aspect ratio h/D=1/100 were used in themodel, FIG. 12D). The relative lattice strain of each structural unitwas evaluated over time, and units at the cylinder edge have the higheststrain up to 0.8% and form a distinct hoop (FIG. 12D). Liftoff viadissolving PMMA exposes the graphene layers and the sandwichedmicrospots to external force fields, led by liquid agitation and heatinduced cavitation. A force balance under a uniform outward stretch(FIG. 12E), assuming no delamination between graphene and the microspotunderneath, can be reduced to

$\begin{matrix}{{{ɛ_{1}(r)} = \frac{2T_{G}{ɛ_{2}(r)}E_{G}}{\left\{ {{2E_{G}T_{G}} + {E_{P}{h(r)}}} \right\}}},{{{and}\mspace{14mu} 4\pi \; {rE}_{G}T_{G}{ɛ_{2}(r)}} = F}} & (1)\end{matrix}$

where ε₁ and ε₂ refer to the graphene lattice strain under tensile forceF, interior and exterior to the microspot, respectively. The microspotheight h (μm) is a function of its radius r (FIG. 12E), and T_(G)represents the graphene thickness. E_(P) and E_(G) are the elasticmodulus of PS (or its composites) and graphene, respectively. Themismatch between the effective elastic moduli of the freestandinggraphene and those laminated to the polymer or its compositesubstantially increase the lattice strain (0.2%) near the microspotradius with a assumed boundary condition of F (r=250 μm)=1.1 mN(corresponding the strain of bilayer graphene=0.1%, FIG. 12F). This,together with the folding dynamics, further augments graphene strain upto 1.0% towards the polymer edges at r=100 μm (FIG. 12F).

The graphene fracture process was numerically simulated with randomizedinitial seed cracks, and observed that this strain heterogeneity canboth attract crack growth, and guide the crack trajectory along themaximum hoop strain (FIG. 12G). This agrees with microscopicmeasurements (FIG. 12H), and recent work that curvature can control thefailure and crack propagation of an elastic polymer sheet at amacroscopic scale³⁴. Lowering h will moderate the strain heterogeneity,thus weakening the autoperforation degree, consisting

with observations that lifting-off microparticle array printed with 0.2wt % PS ink generated a cluster of unperforated microparticles (FIG.30).

TABLE 1 On pristine graphene (FIGS. 33A-33B) PS/ZnO Peak SamplesHeight/nm S1 1415 S2 1258 S3 1348 S4 1199 S5 1275 S6 1008 S7 1318 S81187 S9 1277 S10 1008 S11 907 S12 1047 S13 959 Avg. 1170 St. 158

TABLE 2 On functionalized graphene PS/ZnO Sample Height/nm FS1 1165 FS21061 FS3 1228 FS4 895 FS5 1881 FS6 1353 FS7 725 FS8 812 FS9 1498 Avg.1180 St. 344

TABLE 3 G-PS/BP-G on pristine graphene G-PS/BP-G particles Height 1 8742 888 3 603 4 580 5 592 6 597 7 721 8 725 9 1230 10 1087 11 871 12 86813 858 14 873 15 858 Avg. 815 St. 179

The graphene microparticle has high surface conductivity and canfunction as a two-terminal electronic device when compositing PS with BP(FIGS. 13A-13H). The in-plane conductivity of the G/PS/G microparticleis on the order of 10⁻⁵ S, 10 orders of magnitude higher than that ofthe PS control (10⁻¹⁵ S) (FIG. 13A). The calculated sheet resistance ofthe PS supported graphene is 890 Ω/sq compared to the 4.3×10¹³ Ω/sq forpure PS (FIGS. 13A and 35A-35B and 36), consistent with reported values.See, Yang, J. J. et al. Memristive switching mechanism formetal//oxide//metal nanodevices. Nat Nano 3, 429-433 (2008), which isincorporated by reference in its entirety. The conductivity reduced by33% after storage in ethanol/water (4:1) for four months (FIG. 35D).When applying an electrical potential via a tungsten probe across theG/PS/G particle grounded on top of ITO/glass, a vertical conductivity ofthe order 10⁻⁶ S was measured (FIGS. 13B and 37A-37D). Graphene A and Bcould contact after liftoff, as evidenced by those tails attached to theparticles (FIGS. 11G and 21A).

Interestingly, this conductive mode can be manipulated to anelectrically bistable resistive switch by compositing a very smallamount (0.9 wt %) of liquid-exfoliated BP nanoflakes (1-3 layers, FIGS.17A-17G and 18A-18B) to the PS (FIG. 13B). FIGS. 17E-17F show TEM imagesof the BP nanoflakes at scale of 100 nm and 10 nm, the insert shows thefast Fourier transform (FFT) of the TEM image at the selected area.Atomically structured P arrangements can be seen, echoing the FFT of theTEM image, which suggests the crystalline nature of the BP nanoflakes(see, Yasaei, P., et al., High-Quality Black Phosphorus Atomic Layers byLiquid-Phase Exfoliation. Advanced Materials, 2015. 27(11): p.1887-1892., which is incorporated by reference in its entirety). FIG.17G shows selected area (electron) diffraction pattern (SADP) of BPnanoflakes. SAD patterns are a projection of the reciprocal lattice,with lattice reflections showing as sharp diffraction spots. The scalebar represent 10 l/nm in the reciprocal lattice space.

The G-PS/BP-GS microparticle is essentially a non-volatile reversiblerandom access memory (RRAM) device. FIGS. 13B and 37A-37D show thetypical current-voltage (I-V) characteristics of thistwo-graphene-terminal resistive switch. The device is initially in ahigh resistance state (HRS, i.e., OFF state) and a voltage sweep from 0to 4 V switches the device to a low resistance state (LRS, ON state),corresponding to “writing” a digital memory. A reverse sweep from 0 to−4 V switches the device “OFF”, analogous to “erasing”, and this OFFstate persists until the subsequent 0-4 V sweep in the next cycle.Remarkably, the ON/OFF ratio (N) reaches up to 10⁴ at a 0.2 V readoutvoltage, although the microparticle only contains 0.9 wt % of BP.Graphene is indispensable and PS/BP particle alone is almost insulated(FIGS. 13B and 39A-39B). To further confirm the non-volatile nature ofthis electrical memory, three consecutive low voltage scans were run anda signature sequential step-wise conductivity increase was found(“switch 1” and “switch 2”), and these traces agree well with thediode-memristor model (see, Yang, J. J. et al. Memristive switchingmechanism for metal//oxide//metal nanodevices. Nat Nano 3, 429-433(2008), which is incorporated by reference in its entirety, and FIGS.13C and 40).

The unique chemistry of BP nanoflakes and the percolated structure ofBP/PS composite made this memory. BP nanoflakes degrade and react withoxygen and/or solvent molecules during liquid exfoliation and generatecomplex functional groups with oxygen atoms (e.g., phosphates andphosphonates) on the flake surface or edge (see, Brent, J. R. et al.Production of few-layer phosphorene by liquid exfoliation of blackphosphorus. Chemical Communications 50, 13338-13341, (2014), and Hanlon,D. et al. Liquid exfoliation of solvent-stabilized few-layer blackphosphorus for applications beyond electronics. Nature Communications 6,8563, doi:10.1038/ncomms9563 (2015), each of which is incorporated byreference in its entirety, and XPS results of FIG. 18A). Theseoxygen-containing moieties can act as insulating charge traps initiallyand conductive channels/filaments above a threshold voltage, throughelectromigration of the mobile oxygen vacancies. See, Hao, C. et al.Liquid-Exfoliated Black Phosphorous Nanosheet Thin Films for FlexibleResistive Random Access Memory Applications. Advanced FunctionalMaterials 26, 2016-2024 (2016), which is incorporated by reference inits entirety. Within the BP/PS composite, the atomically thin BPnanoflakes interpolate in between vicinal PS nanoparticles, and form apercolated network, thereby allowing effective resistive switching usinga relatively low BP content (0.9 wt %). Previous work compositingsingle-walled-carbon-nanotube with polymer latex nanoparticles producesconductive polymer nanocomposites with a percolation threshold as low as0.04 wt %. See, Grunlan, J. C., Mehrabi, A. R., Bannon, M. V. & Bahr, J.L. Water-Based Single-Walled-Nanotube-Filled Polymer Composite with anExceptionally Low Percolation Threshold. Advanced Materials 16, 150-153(2004), which is incorporated by reference in its entirety.

Scanning electron microscope (SEM) image of the PS/BP composite in FIG.13D presents the exact morphology of such a network. FIG. 13E is theimage from the energy selective backscattered detector of SEM, which candistinguish elements by atomic number and heavier elements have brightercolors. The isolated dark spots were identified as the carbons from PSnanoparticles among a brighter BP matrix. A scheme (FIG. 13F)illustrates such a percolated BP/PS composite structure and a memristorelement is proposed with graphene layers as terminal electrodes, thepercolated BP (or GO_(x), MoS₂) network as charge trapping (or memorystorage) material, and PS as structural support. Note that the presentedpercolated structure exit vertically at a submicron scale, and amicroparticle with diameter ˜260 μm possesses numerous such BP channelsin between the graphene terminals, that is, it has multiple memristorelements (FIG. 13F). Predictably, by applying a local electricalpotential, one can selectively turn these elements ON or OFF if the BPcharge trapping is effective and the voltage-spreading radius is small.As a demonstration, using a probe with a tip diameter of 5 μm and a“write-read-erase-rewrite” procedure, the letters “M”, “I”, “T” weresuccessfully mapped out contrasting high-conductivity (ON) andlow-conductivity (OFF) states on a 5×3 grid (or 15-bit) inside themicroparticle (FIG. 13G), with an average ON/OFF ratio N≈10⁴.

Interestingly, the long-term memristor behavior of these microparticles,i.e., ON/OFF ratio N, depends on the time they spend in solution (FIG.13H). Microparticles were sampled with various storage times of 0-63days and measured the respective N values for a large number ofcandidates. For each test, N is relatively constant for over 100 cyclesof reversible switching (FIG. 40). FIG. 13H plots all the N valuesmeasured along with their statistics (see histograms in FIGS. 41A-41Gfor details) against storage time t (days), which appears to obey thefollowing equation

N=2.26×10⁴ e ^(−0.10t)  (2)

This yields a half-life of 7 days for the N decay. Therefore, eventhough these microparticles seem to remain their robustness (orsustained N values) upon subjected to water with a relatively shorttime, e.g., 8×10 min (see FIG. 40), water and the dissolved oxygenmolecules in the solution may gradually permeate into the interior BP/PSthrough those intrinsic nanopores in the CVD graphene membrane (see,O'Hern, S. C. et al. Selective Molecular Transport through IntrinsicDefects in a Single Layer of CVD Graphene. ACS Nano 6, 10130-10138,doi:10.1021/nn303869m (2012), which is incorporated by reference in itsentirety), and react with/etch out the superficial BP irreversibly (see,Island, J. O., Steele, G. A., van der Zant, H. S. J. &Castellanos-Gomez, A. Environmental instability of few-layer blackphosphorus. 2d Materials 2, 6, doi:10.1088/2053-1583/2/1/011002 (2015),and Huang, Y. et al. Interaction of Black Phosphorus with Oxygen andWater. Chemistry of Materials 28, 8330-8339,doi:10.1021/acs.chemmater.6b03592 (2016), each of which is incorporatedby reference in its entirety, and XPS results of the fresh and 63 daymicroparticle in FIGS. 41A-41G). This is a relatively slow process dueto the slow reaction rate (see Island, J. O., Steele, G. A., van derZant, H. S. J. & Castellanos-Gomez, A. Environmental instability offew-layer black phosphorus. 2d Materials 2, 6 (2015), which isincorporated by reference in its entirety) and graphene acting as aprotective layer, but will eventually lead the breakdown of BP networkand thus its capability of charge trapping and resistive switching.

The scaling suggests that dissolved oxygen and/or water may graduallypermeate into the BP/PS interior through intrinsic defects and nanoporeswithin the CVD graphene membranes.26 Water and oxygen can react with andetch out superficial BP irreversibly, 27, 28 as evidenced by XPScomparisons between 0 and 90-day microparticles (FIGS. 57A-57B). Using2D materials with fewer of these porous defects may increase thepersistence of N, and therefore information retention. One the otherhand, if the 2D surface layer have controlled nanopore size and density,the use of these microparticles could be a valid nano/micro extractiontechnique to selectively interact and record more sophisticatedchemicals in complex environments.

Digital information can be electrically written to the microparticles bylifting them off as freely dispersing colloids into a solvent likeethanol and then recapturing them with a subsequent read out the writteninformation (FIG. 14E). G-MoS₂ (0.07 wt %)/PS-G was used for thisdemonstration because it is relatively easy to turn on with a voltageabout 2.0 V in the initial run even after a storage time of 2 months(FIG. 96A). Almost an order of conductance increase was observed whencomparing 14 domains with turning-on treatment before and after liftofffrom three different G-MoS₂/PS-G microparticles (FIG. 14F and moredetails in FIGS. 96A-96B). The Wilcoxon signed rank test upon initialand final conductance data confirms such an increase with a p-value of0.0004. On the contrary, the same analysis of the results from 25control domains without turning-on treatment is failed with a p-value of0.2216, meaning a statistically insignificant change (FIG. 97). Theseexperiments support the potential of these microparticles to utilizeinternal or external power to generate or capture information, storingit for a duration in the memristor for read-out at a later time.

The particulate nature of these two-terminal devices renders them theproperty of fluid dispersion, and therefore convective mobility, whichallows one to bring electronics to otherwise inaccessible locations.Applications include “aerosolizable electronics” as probes for remotesensing and recording of environmental information from unconventionalspaces. To test the ability of aerosolization of G-PS-G particles, anairbrush at 1.7 atm (FIGS. 86A-86D) was loaded with a 10-mL dispersionof microparticles and sprayed over 30 cm onto a target collector (FIGS.86A and 59A-59D). A microscope was used to study a sampling of collectedmicroparticles for changes in morphology and deposited location relativeto the ejection centerline. FIG. 86B presents the positions of 460collected microparticles with 80% located isotropically within adistance of 8 cm from this centerline (FIG. 59D). Microparticles appearflexible with some collected samples folded into various 3D structuresduring the nebulization process without fracture, and the survive yieldis approximately 10% lower than that by evaporative drying (FIG. 60).Notably, the graphene surfaces remain intact upon capture (FIGS.61A-61B), preserving the integrity of the device for the furtherwrite-in or read-out electrically. The use of adhesive tapes, such as aflexible paper tape or conductive copper foil tape that can easilytransfer the dried particles out from its initial sitting surface ontothe tape (FIG. 86A). If a copper foil tape is used, in the digitalinformation of the particles can be also read out or written usingprobes (FIGS. 98A-98C).

The unique capability of the autoperforation technology to engineer thesurface chemical functionalities and the interior filler composition ofthe microparticles can further bring the two-terminal electronic devicesdesirable functions. For example, possessing capture sites to reactspecific impurity metals and ions in water samples and soil matrices,respectively, and the good recoverability (FIG. 86B). Specifically,graphene-based microparticles with surface amine groups can interactwith citrate-coated gold nanoparticles in water (˜6.0E+12 particles/mL,10 nm) (FIG. 86B, a), and those with surface nitrilotriacetic acids (NTAligands) can capture Zn²⁺ ions (an essential nutrient for plantgrowth²⁹, 10 mM), while traversing the soil bed (FIG. 86B, b). Suchinteractions change the electrical states of the two-terminal devices,i.e., the amine ones show more than one order of the surface conductanceincrease after bonding gold nanoparticles (FIG. 86C, blue triangles),while the NTA ones have two orders of magnitude reduction upon Zn²⁺capture (FIG. 86C, red triangles). Raman spectroscopy confirms the twobonding events with an observed redshift of the graphene 2D Raman peakabout 3.7 cm⁻¹ (FIG. 86D, blue squares) and a blueshift of the same peakabout 6.2 cm⁻¹ (FIG. 86D, red squares) correspondingly. Besides,incorporating 1.9 wt % iron oxide nanoparticles into the interior fillergenerates ferromagnetic microparticles, and these particles can becaptured and separated with magnets from the extracted water passing therough the soil bed, as compared to a centrifugation separation of G-PS-Gmicroparticles (FIG. 86B).

The graphene microparticles are acid proof and mechanically stable andflexible. For example, G-PS-G can retain their circular shapes aftertreated with a pH=1.5 solution (0.4 M glycine adjusted by concentratedHCl) mimicking human gastrointestinal tract overnight (FIGS. 41A-41G).Besides, the particles can be aerosolized via an airbrush at 1.7 atm(FIGS. 14A-14C and 42A-42G). Specifically, an airbrush was loaded with10-mL dispersion of microparticles, and sprayed onto a collection boardconsisting of 21 glass slides 30 cm away (FIGS. 14A and 41A-41G). Themorphology was studied and the position of the collected microparticleswere located under microscope. FIG. 14B presents the exact locations of˜460 microparticles on the board and 80% of them located at a distance 8cm away from the spraying center (FIG. 14C). The yield is only 10% lowerthan that by natural drying (FIG. 43). These microparticles are flexibleand some of them have folded into different 3D structures like “Taco”“Roll”, “Cone” during the nebulization process, and others withoutbreakage (FIGS. 14B and 43), and most notably, graphene still remains onthe particle surface (see Raman spectra of the collected 10 particles inFIG. 44).

Autoperforation is highlighted as a platform technology that can alsogenerate 2D Janus particles with different surface chemistry and/or 2Dsurfaces (FIGS. 14E and 14F). Functional pyrene or naphthalene molecules(M1-M4 of FIG. 11B, see chemical structures in FIG. 44) containingdifferent functional groups (e.g., —COOH, —NH₂) can modify the two sidesof each graphene film noncovalently (see XPS and water-contact anglecharacterization data in FIG. 43 and Raman spectroscopy results in FIG.44). The surface chemistry symmetry of the particle completely breaksand thus forming Janus particles with four different surfacefunctionalities (FIG. 14A). Functionalization will not affect thecoverage of graphene on the particle (see Raman mapping of the 2D peaksignal in FIGS. 45A-45D) and only slightly change the profile of the PSor its composite microparticles (FIGS. 31A-31D and 32A-32D), but willsignificantly change their appearance. Generally, 2D Janus particleshave “wings” and a better encapsulation of PS (FIGS. 14A and 20B), asevidenced by a yield of 70% even after a storage time of 8 months (FIGS.46A-46D). Functionalization enhances the graphene thickness and thebonding between graphene and the interior filler, and thus reduces thestrain heterogeneity and weakens autoperforation degree, according toeq. (1).

Microparticles were also prepared with various 2D surfaces, likeG/PS/MoS₂, MoS₂/PS/MoS₂ (FIGS. 46A-46D), and hBN/PS/hBN (FIG. 47).Interestingly, the fluorescence imaging of G/PS/G, G/PS/MoS2, andMoS₂/PS/MoS₂ microparticles at λ_(exc)=550 nm shows a stepwise increaseof the photoluminescence (PL) intensity. With only MoS₂ having PL (see,Splendiani, A. et al. Emerging Photoluminescence in Monolayer MoS₂ .Nano Letters 10, 1271-1275, doi:10.1021/n1903868w (2010), which isincorporated by reference in its entirety), G/PS/G is dark without PL,while the latter two both have PL, and the intensity of MoS₂/PS/MoS₂ isalmost twice that of G/PS/MoS₂ (FIGS. 14B and 48A-48C and 49). Inaddition, the minimum feature size of the printed spot can bemanipulated by tuning ink volume, 10 or 1 pL for example, generating asmaller spot with d=34±1.4 and 18.6±2.2 μm, h_(peak)=290±29.8 and 31±9.8nm, respectively (FIG. 14C). Liftoff of the 34-μm spots can generatesmaller microparticles with graphene surface (FIGS. 51A-51B).

In summary, an autoperforation method is developed to guide the fractureof 2D materials, by controlling its strain filed with a sandwichedmicrospot array. Using this method, a free-flowing two-terminalelectronic device was prepared—a microparticle consisting of twographene sheets as surface electrodes and the percolated BP/PScomposites as interior memory storage materials. It functions as anaerosolizable and multi-bit memristor device and the memory behavior(i.e. ON/OFF ratio) depends on its storage time in the aqueousenvironment. The autoperforation is also a platform technology toprepare 2D Janus particles with broken chemical symmetry using various2D surfaces and interior fillers. The autoperforation technology for thescalable development of 2D microparticles can pave the way for nextgeneration free-floating electronics or state-machines that canintegrate into a nanonetwork for complex tasks.

This is the first example of scaling electronics down to amicro-particular level that can survive in harsh conditions. Any othertechnology based “smart dust”, “smart colloidal particles” on the marketor in academia is either orders of magnitude larger than the onesdisclosed herein (2 mm³ as demonstrate by Berkeley recently) or notqualified as electronics (pH sensing colloids using polymer chemistry).This is also the first time that one can fabricate 2d materialelectric/colloidal devices on such a large scale with a lithography-freeindustrially scalable method. There aren't many competing visions inthis space. Immense commercial applications are within reach followed bythe mature development of this technology. Portable micro-meter scaledrandom access memory (RAM) devices as well as “aerosolizable chemicalsensor” are demonstrated, which should both find immediate applicationsin the biomedical and chemical industry space. These devices should findapplications in scavenging environments that are otherwise unattainable:such as in an oil well or human digestive track and relay valuableinformation out.

1. Chemical Vapor Deposition (CVD) Growth of Graphene (G), MoS₂, andHexagonal Boron Nitride

Monolayer and multilayer h-BN (Boron Nitride) film (2″×1″) grown incopper foil was purchased from Graphene Supermarket and used asreceived. Monolayer and bilayer graphene and MoS₂ were grown in the labwith the following procedures:

For Graphene: CVD graphene sheets were produced with a procedure same asin Liu et al. See, Liu, P., et al., Layered and scrolled nanocompositeswith aligned semi-infinite graphene inclusions at the platelet limit.Science, 2016. 353(6297): p. 364-367, which is incorporated by referencein its entirety. Briefly, copper foil (Alfa Aesar, 99.8%, 25 μm thick,for graphene growth) with a size of 2.0×2.2 cm was used as substrate,the copper was annealed at 30 sccm H₂ gas flow (˜560 mTorr) for 30 minat 1000° C. and then 0.5 sccm (for single layer graphene) or 10 sccm(for bilayer graphene, see Tu, Z., et al., Controllable growth of 1-7layers of graphene by chemical vapour deposition. Carbon, 2014. 73: p.252-258., which is incorporated by reference in its entirety) methanewas introduced for 15 min or 10 min, respectively. After that, thefurnace was kept at 1000° C. for another 5 min and turned off. Cu foilwas cooled down and removed out at room temperature.

For MoS₂: Sapphire or SiO₂ substrate (7.0 cm×1.7 cm) washed with acetone(5 min) and isopropyl alcohol (IPA, 5 min) was used in the growth ofMoS₂, MoCl₅ powders (Sigma Aldrich, 99.99%, ˜4 mg) was loaded onto aSiO₂/Si substrate and placed in the central part of the heating zone,the sulfur powder (Sigma Aldrich, 99.998%, ˜0.5 g) was added in aseparate Al₂O₃ boat and placed at the upper stream side of the tubewhere the temperature was about 200° C. during the reaction. Thesapphire or SiO₂ substrate was placed at the downstream side 1 cm nextto MoCl₅. The tube was purged with 50-sccm Ar under vacuum for 30 min,then the furnace was heat to 850° C. in 30 min. The Ar flow kept at 50sccm and the displayed pressure was about 1.13 torr. The tube was keptat the same temperature for another 10 min and then cooled down to roomtemperature naturally.

2. Liquid Exfoliation of the Black Phosphorus (BP)

60 mg of black phosphorus dispersed in 20 mL EG and a tip sonicator witha power of (10% maximum power) sonicated the mixture for 10 hours withliquid cooling at 4° C. to get the exfoliated solution. This solutionwas centrifuged at 2000 rpm at room temperature for 20 min and the finaldispersion of BP nanoflakes was obtained. To determine the concentrationof BP nanoflakes, 1.5 g solution was sampled and filtered using 0.2μm-sized PTFE syringe filter, and weighted the BP nanoflakes left on thefilter after drying under vacuum overnight. The dispersion was dilutedto solutions with different concentrations for the UV-Vis test. Spincoating was used to prepare samples of BP nanoflakes on SiO₂/Si (orgold-coated) substrate for AFM, Raman spectroscopy, and X-rayphotoelectron spectroscopy (XPS) test. A droplet of the dispersion wasadded on to a Holy-carbon grid and dried under vacuum to prepare thespecimen for TEM.

3. The Preparation of Graphene A Layer

In the fabrication, (1) pristine graphene, MoS₂, or hBN grown by CVDmethod directly or alternatively, (2) functionalized graphene were usedto produce Janus particles with a broken chemistry symmetry.

For (1), a PMMA layer was spin-coated around 230 nm onto the surface ofthe graphene/copper foil (or MoS₂/SiO₂) using 950PMMA A4 (MicroChem) at3000 rpm for 1 min. The copper layer (or SiO₂ layer) was etched out withammonium persulfate (APS-100, TRANSENE CO INC) (or 1 M KOH solution at80° C. for SiO₂), and the left graphene (or MoS2)/PMMA film was rinsedwith deionized water. Then Si/SiO₂ substrate was picked up with thegraphene side up (attaching the film from top side of the floating filmon water) or a polydimethylsiloxane (PDMS) stamp (2.5×2.5 cm, 2 mmthickness) which has been attached to the graphene/PMMA layer alreadybefore the etching step.

For (2), a noncovalent functionalization strategy via π-π stacking wasused to modify the graphene layer first before spin coating and etching.Specifically, the copper/graphene (single layer or bilayer) and a sizeof 2.0×2.2 cm was incubated in the dimethyl formamide (DMF) solution offunctional molecules for 1 h and washed with fresh DMF, ethanol, anddried at room temperature (the washing step can remove those excessmolecules which were not attached to the graphene surface). 2 mL DMFsolution of 1-pyrenebutyric acid (97%, Sigma Aldrich), 1-aminopyrene(97%, Sigma Aldrich), 1,5-diaminonaphthalene (97%, Sigma Aldrich), orother functional molecules (2 mmol/L) was added into a 10 mL-beaker withcopper foil, and mechanically shaken for 1 h, then the copper foil wasremoved out and rinsed with DMF and ethanol in sequence, with each of 30s. After drying, following steps including spin-coating, etching, andtransfer are the same as above. For characterization, the film wastransferred onto Si/SiO₂ substrate with the graphene side down andcharacterized with Raman spectroscopy with or without washing out thePMMA layer using acetone, to compare with the pristine graphene.

To functionalize the other side of the graphene film, in this step,methanol, a poor solvent of PMMA was used to prepare the solution offunctional molecules. Functional molecules like 1-pyrenebutyric acidN-hydroxysuccinimide ester (95%, Sigma Aldrich) (4 mmol/L) and 1,5-diaminonaphthalene were used in this step (1-pyrenebutyric acidN-hydroxysuccinimide ester dissolves in methanol at 80° C.). A few dropsof the solution (˜0.5 mL) were added to overcover the surface ofPMMA/graphene film on the SiO₂/Si or PDMS substrate and the incubationtime is 15 min. After that, the film was rinsed with fresh methanol for30s to remove any residual functional molecules that are not attached tothe graphene surface. After drying, the film is ready for the ink-jetprinting in the next step. The SiO₂/Si-supported film was characterizedwith Raman spectroscopy to confirm the functionalization.

4. Ink-Jet Printing of Polymer Latexes or their Composite Solution withNanoparticles

In this step, polystyrene (PS) latex nanoparticles ink or its compositeink with various nanoparticles was printed onto Graphene A to generate amicrospot array. Specifically, polystyrene (PS) latex solutions (SigmaAldrich, PS or amine-modified PS, 0.10 μm or 0.05 μm mean particle size,2.5 wt %) for example, were diluted with ethylene glycol (EG) to 1.2%(vol:vol=1:1), 0.83% (1:2), 0.50% (1:4), and 0.25% (1:9) as inks for theprinting. The PS latex nanoparticles solution was also mixed with zincoxide (ZnO) nanoparticle ink (2.5 wt. %, viscosity 10 cP, work function−4.3 eV, Sigma Aldrich) and further diluted with EG(V_(PS):V_(ZnO):V_(EG)=2:1:1) to prepare ZnO/PS ink; or ironoxide(II,III), magnetic nanoparticles solution (30 nm avg. part. size, 1mg/mL, Sigma Aldrich) and dilute with EG (2:1:1) to prepare magneticnanoparticle/PS ink; or the exfoliated BP solution (0.25 mg/mL, 1:1) toprepare BP/PS ink for printing. In the inkjet printing (MICROSYS,Cartesian Technologies) at room temperature, a ceramic printer needlewas used and the printed ink volume is 1 nL for each dot, the spacebetween the two adjacent dots is 500 μm, and the printing area istypically 1.5-2.0 cm in length and width. After printing, the ink wasdried at room temperature overnight and further under house vacuum for 1h. The printed dot array together with Si/SiO₂ or PDMS-supportedgraphene/PMMA film was annealed at 120° C. for 10 min and cooled down toroom temperature, and ready for the next step. The printer FujifilmDimatrix Materials Printer DMP-2850 was used and an ink volume of 10 pLor 1 pL was printed to prepare smaller-sized microspot with PS latex ink(1.25 wt %, 50 nm mean particle size, in mixture of water and ethyleneglycol (1:1)).

5. The Preparation of the Second Piece of Graphene/PMMA Film (GrapheneB)

Same as the preparation of graphene A above, (1) pristine 2D sheets or(2) functionalized 2D sheets was used to generate graphene B/PMMA filmas the cover layer for stacking. Particularly, one-side functionalizedgraphene/PMMA film in step 4 was transferred onto a relatively largerSi/SiO2 wafer (5×5 cm) with graphene underneath. Drops of the solutionof functional molecules such 1-pyrenebutyric acid N-hydroxysuccinimideester, 1,5-diaminonaphthalene in methanol were added until the completeinfusion of the solution into the underlying surface of thegraphene/PMMA film. The film was incubated for 10 mins and after that,washed with fresh methanol, transferred back to the deionized water, andrinsed with water for 4 times with 10 mins each time. This film wasfloated in water and ready for the next step.

6. Stacking, Liftoff, and Auto Perforation

This stacking and liftoff procedure is the same for the pristinegraphene or functionalized graphene. Specifically, the annealedgraphene/PMMA film on SiO₂ or PDMS substrate with the printed array ofStep 6 severs as the bottom layer to pick up the cover layer of Step 6from water. The two films with the sandwiched microspot array were driedat room temperature for 1 h and then annealed at 120° C. for 15 mins.After that, the films together with the substrate were placed into a50-mL beaker with a magnetic stir bar, 15 mL of ethanol/water (4:1 involume) was added, the beaker was sealed with paraffin and heated to 80°C. under magnetic stirring (1000 rpm) for 10 mins, after that, thesolution was cooled down to room temperature, with visible, darkparticles suspending in the solution. After standing overnight, theseparticles were settled down and the solution was replaced with freshethanol/water (4:1). The heating, stirring, settling down, and solutionreplacement procedure was repeated another two time to remove anyresidual PMMA in the solution or on the graphene surface and after that,these particles were stored in the solution and sampled out on to glassslide, SiO₂ substrate, or ITO-coated glass via dropper for furthercharacterizations or measurements.

7. Microparticles with Molybdenum Disulfide (MoS₂) and Hexagonal BoronNitride (hBN).

The preparation procedure is similar to that of graphene microparticlesabove. The only difference is the transfer of MoS₂ sheet. Monolayer MoS₂grown on Si/SiO₂ substrate was spin-coated with a thin PMMA layer andthe MoS₂/PMMA film was removed out from the SiO₂ substrate using KOHsolution (2 M in water) as etchant at 80° C. The film was rinsed withdeionized water 5 times and used for the further printing and stackingto prepare microparticles with MoS₂ surface. For hBN syncell, singlelayer or multi-layer CVD hBN film grown on copper foil was used, so thetransfer and further preparation of hBN microparticles are the same asthat of the graphene particles above.

8. Characterization and Measurement

The optical images of microparticles were acquired from ZEISS Axio ScopeA1 with magnification of 5 and 20 times. The visualization of theliftoff process was also monitored the same microscope. Ramanspectroscopy was performed on a Horiba Jobin Yvon LabRAM HR800 systemusing a 532 nm excitation laser, 10× objective lens with ˜10 μm diameterspot size, and 1800 lines/mm grating. The profile data of themicroparticles were obtained with Tencor P-16 Surface Profilometer™using a 2 um radius diamond tipped stylus Step height, with ameasurement range of 20 Angstroms to 1 mm. Static water contact anglewas measured by ramé-hart Model 590 goniometer. The transmittance of BPsolution was measured with Shimadzu UV-3101PC Spectrophotometer atwavelength of 660 and 1176 nm, freshly exfoliated BP solution was usedas stock solution and dilute with different times for the measurement.

Atomic force microscopy (AFM) was performed using Asylum MFP-3D-BIO intapping/AC mode with Si tips (Asylum, AC240TS). The scan rate was 0.7 Hzand scan angle was set to be 0°. Black phosphorus (BP) samples wasprepared via spin-coating onto a plasma-treated SiO₂/Si substrate.Scanning electron microscope was conducted on Zeiss MerlinHigh-resolution SEM, which is equipped with an in-lens energy selectivebackscatter detectors for back-scattered electron imaging and thevisualization of regions of different composition. The BP/PS compositesample was prepared via mixing of 100 μL of PS latex nanoparticledispersion (2.5 wt %) and 100 μL of BP dispersion in ethylene glycol(0.25 mg/mL) and drying on hot plate of 120° C. for 10 mins.Transmission Electron Microscopes (TEM) of BP nanoflakes was carried onJEOL 2010 Advanced High Performance TEM and BP nanoflakes were suspendedon holy-carbon grid for the characterization. For the fluorescenceimaging of MoS2 or graphene microparticles, the particles together withsolvent were sampled and naturally dried on glass slides, a broadbandsupercontinuum white light source (NKT Photonics, SuperK EXTREME EXR-15)was attenuated with a neutral density filter. Fluorescence signal wasfiltered with band-pass and collected on a 512×512 pixel imaging area ofelectron multiplying charge coupled device (EMCCD) camera (Andor,iXon3). X-ray photoelectron microscopy (XPS, Kratos AXIS Ultraspectrometer with a monocromatized Al Kα source) was used to analyze thesurface chemistry and compositions of various samples includingmicroparticles with different 2D materials and different storage time,funtinalized graphene, BP nanoflakes, and others.

9. Study the Electrical Properties of Graphene Microparticles with ProbeStation

A MATLAB code was written to execute commands over a semiconductorparameter analyzer (SPA) (Agilent E5262A Source Measure Units), which isused to query electrical information of the microparticles aided by aprobe station. The microparticles were loaded into a probe stationchamber and the electrical measurements were carried out in an ambientenvironment at room temperature with sweeping voltage rate was 50-100mV/s. In general, the electrical properties of these 2D materialsmicroparticles can be categorized into two major modes: in-plane modeand vertical (out-of-plane) mode. In the in-plane mode, themicroparticles are placed onto an insulating surface (typically glass)with one of the 2D material (typically graphene) surfaces facing up, andthe Tungsten (W) probe head gently placed on the material surface. Inorder to aid the process of locating a microparticle under themicroscope atop the probe station, its location is separately locatedunder an optical microscope and marked before it was placed in the probestation. In the vertical mode, vertical conductivities (or through-planeconductivity of the 2D material-composite vertical stack, i.e.Gr-PS/BP-Gr) are typically tested. In this case, a conductive substratefor the microparticle is needed to complete the probe-particle-substratecircuit. ITO substrate was selected for its robustness.

10. Experimental Demonstration of the Potential Application of theMicroparticles 10.1. The Readout, Write in, Liftoff, and ReadoutExperiment

Microparticles G-MoS2 (0.07 wt %)/PS-G after a storage time of 2 monthsin the ethanol solution were used in the experiment. Specifically, a fewdroplets of microparticle solution were sampled and transferred it ontoan ITO-coated glass. After drying the solvent under ambient conditionsand further at vacuum for 1 h, the ITO/glass was placed with thedeposited microparticles onto the probe station. A grid was drawn on thereal-time image of the microparticles on the screen to facilitate thelocation of 12 spots on the microprobe (tip diameter=5 μm) for readingout and the write-in. A voltage sweeping of 0-0.15 V was first appliedto read out the initial conductance status of the 12 spots and laterselectively switching on 6 spots with a voltage sweeping of 0-5 V, andat the same time, keeping the other 6 spots unchanged. After this, theITO/glass was removed out from the probe station and added ethanolsolvent on to the surface to lift off the microparticles on the surface.Mechanical agitation was applied using fine glass tube or needles toassist the liftoff and the liftoff process was also visualized under theoptical microscope. The microparticles will stay in the solution for 10min after liftoff and is dried the solution under ambient conditions andfurther at vacuum again. The conductance of the twelve spots were readout on the probe station by applying a voltage sweeping of 0-0.15 Vagain. Here each microparticle has its own tails or shapes thatdifferentiates it from others so that the same microparticle wasidentified before and after liftoff. The same grid was drawn to locatethe spots with turning on treatment in previous so that the microprobecan read out the vertical conductance change of these same spots afterliftoff for comparison.

10.2. Aerosolization of the Graphene Microparticles Via Airbrush

Aerosolization of the dispersion of graphene microparticles wasconducted with an airbrush (Master Airbrush G222 Pro SET, 0.5 mm setsize) with a working pressure of 1.7 atm (25 psi) and distance of 30 cm.Specifically, 5 mL of microparticles (G-PS-G) solution was loaded andsprayed out using the air pressure generated by an air compressor(Master Airbrush Model C16 Black Mini Air Compressor). Themicroparticles together with the aerosolized solution were flying in airand collected by a board consisting of 21 (7×3) glass sides, which is 30cm away from the airbrush. The microparticles collected by the glideshave been further investigated with optical microscope for counting,morphology study, and position tracking, and Raman microscopy to studythe graphene coverage.

If the collecting slides have a conductive surface, a thin ITO coatinglayer for example, the collected microparticles via eitheraerosolization or natural drying, with the substrate, can be placed ontothe probe station for the direct writing-in and erasing-out of thedigital memory, i.e., using the probe to switch on and off locally. Ifregular glass slides or other materials with an insulating surface wereused, a contact transfer printing method that using an adhesive tape,e.g., conductive copper foil tape was applied to stick onto and transferthe particles out from the insulating surface to the desired copper foiltape. For the demonstration at a macroscopic level, G-PS/GOx (1 wt %)-Gand G-PS/MoS₂(0.07 wt %)-G particles fabricated via capillary printingwith a diameter around 1-2 mm were used, with or without silver. Thedispersion of the particles were sampled and dried on a glass slide, andthen used both paper tape and conductive copper foil tape to conduct thecontact transfer printing on a cm-sized area. In addition, theindividual dried particles can also be picked up and transferred ontothe tape via tweezers.

10.3. Mammalian Digestive Track Test

The mammalian digestive track corrosive environment was mimicked to testthe chemical stability of G-PS-G, an in vitro protocol that was widelyused as the test environment. Specifically, in a SBET (SimpleBioaccessibility Extraction Test) (see Oomen A G, Hack A, Minekus M,Zeijdner E, Cornelis C, Schoeters G, et al. Comparison of Five In VitroDigestion Models To Study the Bioaccessibility of Soil Contaminants.Environ. Sci. Technol. 2002, 36(15): 3326-333, and Ruby M V, Davis A,Link T E, Schoof R, Chaney R L, Freeman G B, et al. Development of an invitro screening test to evaluate the in vivo bioaccessibility ofingested mine-waste lead. Environ. Sci. Technol. 1993, 27(13):2870-2877, each of which is incorporated by reference in its entirety),100±0.5 mL extraction fluid (0.4 M glycine adjusted to pH 1.5 withconcentrated HCl) was added to 1.0±0.5 g of dry weight of things to bedigested. This mixture is rotated end-over-end at 37° C. at 30±2 rpm for1 h. Similarly, G-PS-G microparticles placing on glass slides weretreated with same acidic mixture overnight rather than 1 h.

10.4. Amine Functionalized Graphene Microparticles for the Detection andMemorizing Gold Nanoparticles in the Water Sample

Graphene microparticles (G-PS-G) were used with surface —NH₂functionalities for the demonstration. Briefly, the1,5-diaminonaphthalene-functionalized microparticles in ethanol/water(4:1) solution were concentrated by centrifugation, a small droplet(about 0.1 mL) of the dispersion was sampled out with a large number ofmicroparticles, added it to 2-mL gold nanoparticle solution (˜6.0E+12particles/mL in citrate buffer, Sigma-Aldrich, 10 nm diameter), andincubated for 1 h. The microparticles were then separated from thesolution via centrifugation. After three cycles of washing with freshethanol/water mixture and centrifugation, a droplet of the solution wasfinally retraced out with the dispersed microparticles and placing it onan ITO-coated glass. After drying overnight at vacuum overnight at roomtemperature, the surface conductivity of the microparticles and Ramanspectra of 10 different microparticles were measured for a statisticallystudy.

10.5. Nitrilotriacetic Acid (NTA) Ligand Modified GrapheneMicroparticles for the Detection and Memorizing Zn²⁺ Concentration inSoil

To demonstrate the ability to deploy these microparticles to function asstand-alone detectors in this practical scenario, both outer surfaces ofthe graphene layer of the microparticles were non-covalentlyfunctionalized with the nitrilotriacetic acid (NTA) ligand, and turnthem into retractable sensor nodes for trace amounts of Zn²⁺ ionspresent in the ground soil, which is a crucial plant micronutrient thatinvolves in many physiological functions of plants. Specifically, themicroparticles were fabricated with polystyrene (PS)—Fe₃O₄ magneticnanoparticle composite core, flanked by two double-layer graphene sheetson the top and bottom, following the standard procedure introducedpreviously. To functionalize the NTA ligand onto the outer surface ofthe graphene layers, a pyrene-containing linker,1-pyrenebutyricacid-N-hydroxysuccinimide ester (Sigma Aldrich), thenreacted with N,N-bis(carboxymethyl)-L-lysine hydrate (Sigma Aldrich)were used at room temperature, after adjusting the pH to 9.0, using anNHS ester amine-reactive cross-linking chemistry.

III. Modeling of the Autoperforation Process

A. Strain Guided Fracture Propagation with Stochastic Seed CrackFormationa. An Existing Model

There is an existing model on soft material fracturing within a strainfield induced by curvature.

B. Algebraic Estimation of the Tensile Strain Due to Material Thicknessand Elasticity

a. Model Derivation

There will be fluctuating tensile stretches in the graphene lattice oncethe PMMA layer is removed by the ethanol/water solution due to turbulentfluid flow. The primary purpose of this section is to estimate thestrain distribution due to this random stretching/compressing of thefree-standing graphene lattice by the external forces.

1. Consideration of a 2D Slice

To get started, a simple 2D slice is considered to find the relationbetween strain and elastic moduli of materials involved as well as theirthickness, as informed by the vertical profile measurement of themicroparticle (FIG. 64A).

This concave-down dough shape is captured by the sketched profile (FIG.64B), where a BP/PS dough is considered being encapsulated within twobilayer graphene sheets. If one imagines a force F pulling on such asandwich structure of width w on either side, then a force balance canbe obtained:

2F=E _(Gr)ε₂(r)2T _(Gr) w=ε ₁(r)E _(PMMA) h(r)w+ε ₁(r)E _(Gr)2T _(Gr)w  (9)

where F is the magnitude of force F, and ε₁, ε₂ are the materialrelative strain for Gr-BP/PS-Gr composite and Gr-Gr, respectively. NotePS was used to approximate the BP/PS composite, which is reasonableconsidering BP's low concentration within the PS matrix. This yields thefollowing relationship:

$\begin{matrix}{\frac{ɛ_{2}(r)}{ɛ_{1}(r)} = \frac{{2E_{Gr}T_{Gr}} + {E_{PMMA}{h(r)}}}{2E_{Gr}T_{Gr}}} & (10)\end{matrix}$

which relates the relative strain outside the PS microspot to thatwithin. Now that all is needed is to set an appropriate boundarycondition to correctly evaluate the force F.

1. A Radially Symmetric 3D Model

By taking advantage of radial symmetry, one can easily generalize this2D slice into a 3D model. It should be noted that since there is lessand less material towards the middle of the microparticle, in order towithstand the same amount of force outward (which is clearly conserved),then materials closer to the center need to be stretched more, therebyhaving a larger strain. Without loss of generality, the center of themicroparticle was set as the origin of the cylindrical coordinates, itthen follows from Eq. (10) and the corresponding 3D force balance,

$\begin{matrix}{{{ɛ_{1}(r)} = \frac{2E_{Gr}T_{Gr}ɛ_{2}^{R_{F}}R_{F}}{\left\{ {{2E_{Gr}T_{Gr}} + {E_{PMMA}{h(r)}}} \right\}}},{{{where}\mspace{14mu} ɛ_{2}^{R_{F}}} = \frac{F}{4\pi \; R_{F}T_{Gr}}}} & (11)\end{matrix}$

where ε₂ ^(RF) is defined as the relative strain at which force ofmagnitude F is applied to the ring of materials at radius R_(F). And ifR_(F)=250 μm and ε₂ ^(RF)=0.1% is set, and to approximate the doughshape of the microparticle, its vertical profile is approximated as:

$\begin{matrix}{{h(r)} = {{\frac{1}{R_{0}}\sqrt{R_{0}^{2} - r^{2}}} + {2T_{Gr}}}} & (12)\end{matrix}$

where R₀ is the radius of the PS microspot, which is set to 100 μm tothe best estimation. This model yields a strain contour for the graphenematerials that shows maximum strain built-up right outside the microspot(FIG. 63A), with the height profile shown in FIG. 63B. FIG. 63A showsthe well-dispersed BP nanoflakes/EG solution follows Lambert-Beer law atλ=660 and 1176 nm, with the extinction coefficient (α)=80.3±3.0 Lg⁻¹ m⁻¹and 62.0±2.7 Lg⁻¹ m⁻¹, BP concentration (C_(BP)) was determined viafiltration method. In FIG. 63B, the three sharp Lorentzian-shaped peaksdemonstrate the crystalline nature of BP nanosheets (see, Kang, J., etal., Solvent Exfoliation of Electronic-Grade, Two-Dimensional BlackPhosphorus. ACS Nano, 2015. 9(4): p. 3596-3604, which is incorporated byreference in its entirety). This tensile strain, in additional to thefolding strain discussed in the previous section, combines into a totalstrain field which is followed by a strain induced crack propagationthat finishes the auto-perforation process.

C. Finite Element Coarse Grained MD Simulation for Mold-Based GrapheneFolding

a. Overview

A theoretical model that simulates the kinetic process involved in thefirst step of the autoperforation of bi-layer graphene during themicroparticle fabrication process is developed. A mathematical modelimplemented in MATLAB allows us to predict the shape of the system afterthe first step as well as where the graphene sheets are most strained. Amore thorough understanding of the mechanics of autoperforation, and howvarying parameters affect the resultant shape, is crucial in order to beable to design customizable microparticles of different shapes, sizes,and materials.

b. Theoretical Considerations

1. A Kinetic Process

This model numerically solves the differential equations of motion thatgovern the auto-perforation process. The advantages of a kinetic model,as opposed to a thermodynamic—or equilibrium—model, are that it allowsus to observe the kinetic trapped states during graphene folding.Additionally, there is an option in the model that allows graphene totear once it reaches a certain specified strain.

2. Spring Force

The 2D sheet is broken down into a square lattice with nodesrepresenting material points, each node accounting for the mass of allthe materials within that unit lattice. Each node experiences a springforce from each of its four neighbors. For a material with linearelasticity, such as PMMA, this force F_(LS) is:

F _(LS) =EεA ₀  (1)

where E is the Young's modulus of the relevant material, E is thestrain, and A₀ is the cross sectional area of the section. However,graphene is known to have a nonlinear elasticity, and the non-linearspring force a node feels from one of its neighbors, F_(NLS) is:

F _(NLS)=(Eε+Dε ²)A ₀  (2)

where D is a third order elastic modulus to account for thenon-linearity, and typical values for E_(Gr) and D_(Gr) are 1.0 TPa and−2.0 TPa, respectively. In this model, the material connecting the nodesis a two-layer composite of PMMA and graphene, which is modeled as twoparallel springs, giving the total spring force F_(S):

F _(S)=(E _(Gr) ε+D _(Gr)ε²)T _(Gr) L ₀+(E _(PMMA)ε)T _(PMMA) L ₀  (3)

where T_(Gr) and T_(PMMA) are the thicknesses of the graphene and PMMAlayer, respectively, and L₀ mesh size perpendicular to the forcedirection.

3. Van Der Waals Force

Van der Waals forces are weak intermolecular forces that arise due topermanent and induced dipole moments in molecules. Each particle in thismodel experiences attractive van der Waals forces towards the bottomsheet of graphene, and also to the polystyrene pellet. The potential forthe surface-surface interaction (per unit area), W, is given by,

$\begin{matrix}{W = \frac{- H}{12{\pi\delta}^{2}}} & (4)\end{matrix}$

and the corresponding van der Waals force, F_(vdW), is

$\begin{matrix}{F_{vdW} = {{- \frac{dW}{d\; \delta}} = \frac{{HL}_{0}^{2}}{6{\pi\delta}^{2}}}} & (5)\end{matrix}$

where H is the Hamaker constant, and δ is the distance between the twointeracting surfaces. The surface-surface interaction is the mostappropriate for this model (as opposed to an atom-surface orsphere-surface interaction), since the discretization of the graphenesheet produces planar units with large aspect ratios.

4. Capillary Interaction

Capillary forces (i.e. water-graphene attractive interactions) play alarge role in many graphene folding and transfer applications. However,the exact nature and magnitude of the capillary interaction betweenwater and graphene is not well understood, and is the topic of manydifferent studies. The binding energy W_(adh) for water on bilayergraphene is 58.9±1.9 mJ·m⁻². Further, the maximum traction reported byone study is σ_(m)≈90 MPa. This traction due to capillary forces iscrucial to the first step of the auto-perforation process.

5. Gravity

Gravity acts on all particles, given by Newton's second law, F_(g)=mg,where g is the acceleration of gravity, and m is the mass of one node.The mass of one node is found by dividing the total mass of the systemby the number of nodes in the system:

$\begin{matrix}{m = \frac{\left( {{T_{Gr}\rho_{Gr}} + {T_{PMMA}\rho_{Gr}}} \right){LW}}{N}} & (6)\end{matrix}$

where ρ_(Gr) and ρ_(PMMA) refer to material densities, and N is thenumber of nodes in the system.

6. Viscous Dissipation

The Reynolds number is a non-dimensional number that represents theratio of inertial to viscous forces in a fluid. The Reynolds number ofthe composite folding system, Re, at 20° C. is given by:

$\begin{matrix}{{Re} = {\frac{\rho \; {vL}}{\mu} = {\frac{998.2\mspace{14mu} {{kg} \cdot m^{- 3}} \times 10^{- 6}{m \cdot s^{- 1}} \times 10^{- 4}m}{1.002 \times 10^{- 3}m^{3}} \approx 10^{- 4}}}} & (7)\end{matrix}$

where μ is the dynamic viscosity of the liquid, and ν is the velocity ofa given node. The Re<<1 means that viscous effects cannot be ignored.Therefore, a Stokes' drag force F_(d) acting opposite to sheet'sdownward velocity is included:

F _(d)=6πμRv  (8)

where R is the Stokes' radius (approximated as the thickness of the PMMAsupport layer). The graphene sheet does not actually fall through water,the Stokes' drag is meant to account for the fact that water isdisplaced.c. Model Implementation

1. Nodes and Springs

The structure of this model is an extended system of nodes and springs.For a square mesh with n nodes on a side, there are a total of n² nodestotal, and 2n(n−1) springs since n(n−1) springs are initially parallelto each of the x and they directions. Note that if the nodes arecontained in a 2D array, the ordered pair (i,j) is equivalent to (row,column). Additionally, the nodes are numbered from 1 to n², startingwith (1, 1) and ending with (n_(x), n_(y)). This is because the ordinarydifferential equation (ODE) solvers work with 1D vectors of variables.However, it is much more concise and efficient to work with thesevariables in a 2D array, and then convert it to a 1D vector right beforecalling the ODE solver. These naming conventions are needed in order toprecisely define the relationship between the 1D and 2D representations.

2. Periodic Boundary Conditions

This model utilizes a periodic boundary condition. This means that the“unit cell” modeled behaves as if it was repeated infinitely on allsides. Specifically, edge nodes are nodes with i=1, i=n_(x), j=1, orj=n_(y). Most nodes have four springs attached to them, but these edgenodes only have two or three. The periodic boundary condition isachieved by modifying the forces felt by edge nodes so that the“missing” forces are taken from the opposite side of the unit cell. Forexample, node (i, n_(y)) has no neighbor to the right; there is no node(i, n_(y)+1). The spring force node (i, n_(y)) feels to the right isthen the same force that node (i, 1) feels to the right. In the code,this is implemented by using logic to determine if a node is an edgenode, and if so substituting the missing forces with forces from theopposite edge. The periodic boundary condition has the effect of fixingthe edge nodes in the x-y plane. This is because the edge treatmentdescribed above treats opposite edge nodes as the same point—when theunit cell is repeated, the edges overlap. Intuitively, this also makessense because in an infinitely extended grid of microparticles, the edgenodes lie exactly halfway between two microparticles.

d. Results Summary

The output of this model is the shape of the graphene/PMMA sheet duringand after the folding process. This section is intended to show resultsobtained from the model and in this example, a 250×250 mesh is used,with an aspect ratio of 1:100 (microcylinder height to radius). Thislevel of resolution is needed in order to observe the shape of theresulting profile in the region near the edge of the polystyrene pellet.

Using the native values of the materials (250 nm thick PMMA and 0.67 nmbilayer graphene composite) and the appropriate microspot form factor, amaximum of 0.78% relative strain was obtained within the composite filmright outside of the microspot edge, which hence forth shall be referredto as the “folding strain” (FIGS. 62A and 62B). FIGS. 62A-62B showeffect the ink composition in the inkjet-printing process, adding 50%ethylene glycol into the ink can reduce the evaporation speed of thesolvent and thus suppress the formation of coffee ring (see Kim, D., etal., Direct writing of silver conductive patterns: Improvement of filmmorphology and conductance by controlling solvent compositions. AppliedPhysics Letters, 2006. 89(26): p. 264101, which is incorporated byreference in its entirety). The strain is built-up over time (FIG. 62C),and stabilizes into either an equilibrium or kinetically-trappedequilibrium state.

IV. A Semi-Empirical Model for the BP/PS Composite Memresistors 1.Theoretical Construct

This model is adapted from the seminal work by Stewart and Williams et.al. in the Hewlett-Packard laboratories, where an equivalent circuitmodel consisting of a rectifier in parallel with a memristor isconstructed (FIG. 65A). For each of these microparticle memristorelement, the following equation describes its I-V switchingcharacteristics, derived from the equivalent circuit:

I=I _(m) +I _(r) =w ^(n)β sin h(αV)+χ{exp(γV)−1}  (13)

which is chosen more for its simplicity and ability to reproduce the I-Vbehavior than as a detailed physics model. In the first term, I_(m),which represents a flux-controlled memristor, β sin h(αV) is theapproximation used for the ON state of the memristor, which isessentially electron tunneling through a thin residual barrier; α and βare fitting constants that are used to characterize the ON state, and wis the state variable of the memristor. In this case w is proportionalto the applied electric field. The second term in Eq. (13), I_(r),represents the I-V character for the rectifier, and χ and γ are thefitting constants used to characterize the net electronic barrier whenthe memristor is switched OFF. The exponent n of the state variable isused as a free parameter in the model, which is adjusted to modify theswitching between the ON and OFF states of the device to be consistentwith the experimental observations. A large n is typically interpretedas evidence for a highly nonlinear dependence of the effective vacancydrift velocity on the voltage applied to the device.

2. Model Implementation

In order not to limit the scope of search space for the curve fitting,nonlinear programming was used to locate the minimum of theunconstrained multivariable objective function. The objective functionsthemselves are simply sums of least square differences between the I-Vcurves derived from Eq. (13) and experimental data. This semi-empiricalmodel is capable of fitting, to great success, all the I-V behaviors forthe two-terminal memristors tested, and some of the fits are shown hereas an example (FIGS. 65B-65D).

Experimental data are represented as solid red lines, and model fits asblack dashed lines.

These fittings yield parameters that can provide deeper insights towardeach memristor element. For instance, a closer inspection of the fittingparameters (Table 4) for data presented in FIGS. 65A-65D, which arecollected for a progressively switched-on memristor, offers qualitativeagreement between theory and the nature of the device.

TABLE 4 Fitting parameters corresponding to FIGS. 65B-D. Parameters B CD n 2.30E+00 1.31E+00 2.67E+00 β 2.01E+04 8.75E+03 1.99E+04 α 1.86E+001.96E+00 2.44E+00 χ 1.33E+01 5.32E+05 8.50E+05 γ 4.41E+00 6.68E−026.42E−02

If the left term I_(m)=w^(n) sin h(αV) is compared with the α values, itis observed an increase of α as the memristor is switched from an OFFstate to an ON state. Mathematically, the smaller α is, the furtheralong in the V-axis does the I_(m) start to kink up, meaning the morevoltage it requires to turn the memristor ON. As more charges are putinto the memristor, the memristor is closer to its ON state, whichcoincides with the experimental observation. If the second termI_(r)=χ{exp(γV)−1} that characterizes the rectifier component is focusedon, this is just a recast of the Shockley diode equation, where χ isknown as the reverse bias saturation current (or OFF state current), andγ is just the inverse product of the ideality factor and the thermalvoltage. In the first run, the reverse bias saturation current isnotably smaller and the diode is much closer to ideal. Both of theseobservations agrees with the fact that the memristor is initially in theOFF state.

Micrometer-Size Electrical State Machines Based on 2D Materials forAerosolizable Electronics

Reduction in machine size down to micrometers will dramatically decreasetheir fabrication cost, along with yielding the possibility to exploreenvironments that are too small or too dangerous for humans or largerrobots. To date, the development of such machines was hindered by bothenergy-thirsty electronics and limited, on-board energy storagecapacity. Disclosed herein is a syncell, a micrometer-size particlecapable of changing their electronic state. Compared to thestate-of-the-art millimeter-size robots, the syncell's size shrinkage isenabled by developments in 2D materials that considerably reduceoperational power requirements. The syncell state machine (100×100×5μm³, making them invisible to the human eye) is composed of a powersource, a switch, and a memory element that form a closed electroniccircuit. This circuit remains operational even after travelling inside aturbulent droplet a distance of 0.6 m in air. Syncells successfullydetect analytes while in air and store this information in the memoryusing power harvested by a photodetector. This layout represents aconcept of aerosolizable electronics with particles that can bedispersed in air while having active electronics on-board. To facilitatesyncell collection, syncell standoff detection was realized withon-board retroreflectors. These aerosolizable electronics will allowrapid and cheap monitoring of viruses, bacteria, and fumes that spreadover large areas.

Today there are two main tendencies in the field of micromachines:micro/nanoparticles and biorobotics. Decades of chemical synthesis haveled to the development of complex core-shell particles withmultifunctional capabilities that are widely used for drug delivery,biosensing, imaging, etc. See, Bao, G., S. Mitragotri, and S. Tong,Multifunctional Nanoparticles for Drug Delivery and Molecular Imaging.Annual Review of Biomedical Engineering, 2013. 15(1): p. 253-282, whichis incorporated by reference in its entirety. Although micro- andnanoparticles are relatively simple to synthesize, they aresignificantly limited in their integration capability with conventionalelectronics and their development of complex logical operations.Biorobotics based on genetic engineering, in turn, was able to harnessbacterial life and viruses to create micromachines. See, Smanski, M. J.,et al., Synthetic biology to access and expand nature's chemicaldiversity. Nat Rev Micro, 2016. 14(3): p. 135-149, and Ravi, S. K. andS. C. Tan, Progress and perspectives in exploiting photosyntheticbiomolecules for solar energy harnessing. Energy & EnvironmentalScience, 2015. 8(9): p. 2551-2573, each of which is incorporated byreference in its entirety. Nevertheless, genetic engineering is alsolimited by intrinsic cell architecture and design. As an alternative,micro-scale electrical systems can be made from scratch with theirarchitecture being optimized to the application at hand.

Cubic millimeter-size devices, called “smart dust”, are the smallestdispersed electronic devices reported to date. See, Seo, D., et al.,Wireless Recording in the Peripheral Nervous System with UltrasonicNeural Dust. Neuron, 2016. 91(3): p. 529-539, which is incorporated byreference in its entirety. While the initial concept was developed morethan 15 years ago, further progress was hindered by the lack ofefficient energy storage technologies. Indeed, light-weight batteries donot provide enough power, often forcing small robots to rely on externalenergy harvesting. To this end, some versions of smart dust harvestedenergy from electromagnetic wireless radiation, limiting the devices'operation to a distance of a few meters. See, Seo, D., et al., WirelessRecording in the Peripheral Nervous System with Ultrasonic Neural Dust.Neuron, 2016. 91(3): p. 529-539, which is incorporated by reference inits entirety. Unfortunately, this approach cannot be scaled down, due toreceiver size limitations. See, Seo, D., et al., Model validation ofuntethered, ultrasonic neural dust motes for cortical recording. Journalof Neuroscience Methods, 2015. 244: p. 114-122, which is incorporated byreference in its entirety. Alternative energy harvesting techniques(chemical power harvesting, bacteria-produced power, ultrasound,magnetic field and light) are continuously being developed, deliveringmicrowatts of power on the micrometer scale but, so far, have had littleto no success in powering energy-thirsty electronics (usually requiringmilliwatts). See, Zebda, A., et al., Single Glucose Biofuel CellsImplanted in Rats Power Electronic Devices. Scientific Reports, 2013. 3:p. 1516, Kim, H. and M. J. Kim, Electric Field Control ofBacteria-Powered Microrobots Using a Static Obstacle AvoidanceAlgorithm. IEEE Transactions on Robotics, 2016. 32(1): p. 125-137,Servant, A., et al., Controlled In Vivo Swimming of a Swarm ofBacteria-Like Microrobotic Flagella. Advanced Materials, 2015. 27(19):p. 2981-2988, and Chang, S. T., et al., Remotely powered self-propellingparticles and micropumps based on miniature diodes. Nat Mater, 2007.6(3): p. 235-240, each of which is incorporated by reference in itsentirety.

In a micrometer-size electronic state machines, or a “syncell” (anallusion to the biological term synthetic cell—minimal cell), the issueof energy deficiencies is circumvented using novel 2D devices thatrequire only microwatts, or even nanowatts, of power. Built from 2Dmaterials, these devices are only a few atoms thick, enabling a highintegration density. Note that 2D devices are still in their infancy:Most publications to date demonstrate individual 2D devices fabricatedon flat silicon wafers. See, Wang, Q. H., et al., Electronics andoptoelectronics of two-dimensional transition metal dichalcogenides. NatNano, 2012. 7(11): p. 699-712, Radisavljevic B, et al., Single-layerMoS2 transistors. Nat Nano, 2011. 6(3): p. 147-150, Lopez-Sanchez, O.,et al., Ultrasensitive photodetectors based on monolayer MoS2. Nat Nano,2013. 8(7): p. 497-501, Cheng, R., et al., Electroluminescence andPhotocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunctionp-n Diodes. Nano Letters, 2014. 14(10): p. 5590-5597, and Lopez-Sanchez,O., et al., Light Generation and Harvesting in a van der WaalsHeterostructure. ACS Nano, 2014. 8(3): p. 3042-3048, each of which isincorporated by reference in its entirety. Here, a complete electroniccircuit composed of 2D devices is assembled, forming a 2D state machinethat is operational when lifted-off of silicon.

Large area monitoring of various bacteria, spores, smokes, dust, andfumes is an important task, which currently requires a lot of resources.See, Hansen, M. C. and T. R. Loveland, A review of large area monitoringof land cover change using Landsat data. Remote Sensing of Environment,2012. 122: p. 66-74, which is incorporated by reference in its entirety.In one implementation, satellite scanning can rapidly cover large areas,but it is costly and indirect (this translates into limitedapplicability). On-ground sensor installation is labor-intensive and canoften be slow in comparison to analyte distribution. Employing a fleetof flying sensors (e.g., drones) is again associated with high costs. Asan alternative, the concept of aerosolizable electronics is introduced.Syncells dispersed in the air carrying 2D electronic devices that remainoperational even in flight. Air drag calculations demonstrate that thesesyncells will have <1 cm/s sedimentation speed (FIG. 70; compare thiswith 1 m/s for millimeter-size particles), potentially allowing them tofloat in air for several days without the need of external power. It isexperimentally demonstrated how flying syncells can detect analytesdispersed in air, store this information in the on-board memory (powerfor this is delivered to the syncell via light), and be detected fromstandoff distances using a laser-scanning setup.

Syncell Design and Fabrication

Due to their high aspect ratio, micrometer-scale 2D materials have lowmechanical stability that limits their application off-substrate. Tocircumvent this, a syncell base that plays a role of the carriersubstrate for 2D devices was designed. The syncell base material is acritical choice: It should remain stable during various fabricationstages (2D material transfer, patterning, lift off, etc.) that oftenrequire development steps in different solvents. Using the SU-8photoresponsive polymer, it can be processed with micrometer precisionand becomes very stable after crosslinking. Conventionalphotolithography allows syncell bases' fabrication in different shapesand sizes that can be targeted for different designs and applications(FIG. 71). These fabricated bases (100×100×5 μm³) demonstrate surfaceRMS roughness <5 nm, providing smooth surfaces for 2D devices (FIGS.72A-72C). By etching away the silicon substrate, syncell bases can befurther released from the substrate.

To demonstrate the performance of the electrical circuit on the syncellbase, an electrical state machine was designed with elements ofcombinational logic. To this end, three components have been chosen: apower source, a switch, and a memory element that are implemented by aphotodetector, a chemiresistor, and a memristor, respectively (FIG.66B). These components have to fulfill two important aspects: powerrequirements (they should operate under power that can be harvested,stored, or delivered to a syncell) and material requirements (2Dmaterials should be chosen from the ones that can be grown over largearea to fabricate multiple identical syncells). As a solution, thephotodetector is built based on a p-n heterojunction of MoS₂ and WSe₂monolayers. Another MoS₂ monolayer serves as a chemiresistor thatchanges its conductance upon the binding of external analytes. Finally,the memristor is composed of MoS₂ flakes sandwiched between gold andsilver electrodes. A high-throughput clean room fabrication process isdeveloped to assemble these components into the 2D electrical circuit,producing >2500 syncells in one batch (FIGS. 66A and 73). The syncelloperates in the following way: the photodetector generates voltage onlyif it is illuminated with light; the chemiresistor switches itsconductance after the analyte binding; the memristor changes its statefrom OFF to ON if the applied voltage from the photodetector exceeds athreshold voltage. This configuration can be used as a state machine,using light and analyte as two inputs and the memory state as an output.This can be summarized as two IF blocks and the logic operator AND onthe block diagram: The syncell memory changes its state from OFF to ONif both light shines on the photodetector and the analyte binds to thechemiresistor (FIG. 66C).

Basic Components

The performance of electronic devices changes when they are removed froma native substrate due to the imposed stretch and strain, however 2Dmaterials possess higher strain limits as compared to the conventionalIII-V materials. See, Salvatore, G. A., et al., Wafer-scale design oflightweight and transparent electronics that wraps around hairs. NatureCommunications, 2014. 5: p. 2982, and Akinwande, D., N. Petrone, and J.Hone, Two-dimensional flexible nanoelectronics. Nature Communications,2014. 5: p. 5678, each of which is incorporated by reference in itsentirety. To explore the performance of the devices, syncells weretested in three configurations: (1) as-fabricated on the siliconsubstrate, (2) after liftoff, and (3) after spraying using a nebulizeracross a 0.6 m distance in a 0.15 m diameter tube (FIGS. 74A-74E). Afterliftoff, syncells can be occasionally bent or aggregated due to thecapillary forces during drying (FIGS. 75A-75B). In a typical nebulizerexperiment, using the microscope N=244 syncells had landed on the targetat the other end of the tube, with most of them concentrated in 0.06 mdiameter circle and having no preferential angular direction (FIGS.76A-76C). Droplets ejected by the nebulizer have 7-100 m/s initial speedand <0.3 mm diameter. Numerical calculations show that such momentumallows them to travel 3.0-3.8 m (with travel times <3 ms) before thecomplete stop (FIGS. 77A-77C). Water droplets of this size dry within25-160 sec, supporting that the droplets do not dry during flight.

To test individual components, separate syncells were fabricated withisolated devices. The first component is the photodetector, serving as aphotocell: It converts light into electrical current that, in turn, canbe used to power other 2D components. The 2D photodetector is made of ap-n photodiode comprised of MoS2 and WSe2 monolayers with goldenelectrodes in a 90° configuration with the minimal distance of ˜10 μm(FIGS. 67A and 67B). Photoluminescence measurements, AFM, and Ramanmapping were performed (FIGS. 78A-78E and 79A-79E)—all confirming thecontinuous nature of the MoS₂ and WSe₂ monolayers. When MoS₂ istransferred onto WSe₂, a photoluminescence shift from 760 nm to 800 nmwas observed (FIGS. 80A-80B) that corresponds to a staggered gap (typeII) heterostructure (see Fang, H., et al., Strong interlayer coupling invan der Waals heterostructures built from single-layer chalcogenides.Proceedings of the National Academy of Sciences, 2014. 111(17): p.6198-6202, which is incorporated by reference in its entirety), provingsuccessful formation of a p-n junction. The photodiode showsphotocurrent generation under laser illumination, reaching ε=0.30 V opencircuit voltage and I_(sh)=0.15 μA short circuit current under 532 nmlaser 7 μW/μm² (FIGS. 67C, 67D and 81A-81F), which is comparable to thestate-of-the-art values. See, Cheng, R., et al., Electroluminescence andPhotocurrent Generation from Atomically Sharp WSe ₂ /MoS ₂Heterojunction p-n Diodes. Nano Letters, 2014. 14(10): p. 5590-5597, andYe, L., et al., Near-Infrared Photodetector Based on MoS ₂ /BlackPhosphorus Heterojunction. ACS Photonics, 2016. 3(4): p. 692-699, eachof which is incorporated by reference in its entirety. By testing N=20random devices, photodetectors retain their characteristics afterliftoff (ϵ=0.27±0.05 V, I_(sh)=0.20±0.01 μA), and after spraying(c=0.24±0.05 V, I_(sh)=0.19±0.01 μA) as compared to the on-substratedevices (c=0.27±0.06 V, I_(sh)=0.15±0.01 μA).

The second component is the chemiresistor. It consists of a MoS₂monolayer that changes its electrical conductance upon molecularadsorption (FIGS. 67E and 67F). It is designed to act as a turn onswitch in the state machine. To this end, MoS2 has to increase itsconductance, which can be achieved by choosing an analyte with n-typedoping. As one example, 10 mM triethylamine (TEA) sprayed on MoS₂increases its conductance (FIGS. 67G and 67H): from G_(ch)^(in)′=19.8±2.3 nS to G_(ch) ^(ƒ)=34.7±2.8 nS on the silicon; fromG_(ch) ^(in)=21.1±5.5 nS to G_(ch) ^(ƒ)=36.1±5.5 nS for lifted off; fromG_(ch) ^(in)=20.5±6.6 nS to G_(ch) ^(ƒ)=35.0±6.4 nS for sprayed syncells(the second nebulizer located at the top of the tube was used to spraythe analyte across the syncell movement direction, FIG. 74E). Tounderstand the reaction kinetics, MoS₂-TEA reaction constants wereextracted by analyzing continuous conductance measurements of the MoS₂chemiresistor (see Perkins, F. K., et al., Chemical Vapor Sensing withMonolayer MoS2. Nano Letters, 2013. 13(2): p. 668-673, which isincorporated by reference in its entirety): binding constantk_(ƒ)=0.024±0.001 s⁻¹·μM⁻¹, dissociation constant k_(b)=0.23±0.01 s⁻¹,and irreversible constant k_(i)=0.06±0.01 s⁻¹ (FIGS. 82A-82B and seekinetics details). The process of MoS2-TEA charge transfer is limited bythe surface coverage, providing the maximum of 95% of MoS2 resistancechange. See, Mouri, S., Y. Miyauchi, and K. Matsuda, TunablePhotoluminescence of Monolayer MoS ₂ via Chemical Doping. Nano Letters,2013. 13(12): p. 5944-5948, which is incorporated by reference in itsentirety.

The third component is a memristor. It needs to operate with voltagesharvested by the photodetector. To date, most memristors operate in the1-3 V range (far higher than what the photocell can harness). See, Hao,C., et al., Liquid-Exfoliated Black Phosphorous Nanosheet Thin Films forFlexible Resistive Random Access Memory Applications. AdvancedFunctional Materials, 2016. 26(12): p. 2016-2024, Wang, W., et al., MoS₂ memristor with photoresistive switching. Scientific Reports, 2016. 6:p. 31224, and Sangwan, V. K., et al., Gate-tunable memristive phenomenamediated by grain boundaries in single-layer MoS2. Nat Nano, 2015.10(5): p. 403-406, each of which is incorporated by reference in itsentirety. Only one example satisfies the requirements (see, Bessonov, A.A., et al., Layered memristive and memcapacitive switches for printableelectronics. Nat Mater, 2015. 14(2): p. 199-204, which is incorporatedby reference in its entirety): A MoS₂ memristor fabricated between goldand silver electrodes (FIGS. 67I and 67J; with a size of 25×25×0.1 μm³)has a turn on voltage ˜0.15 V, 100 MΩ starting resistance, and itson/off ratio can reach millions (FIGS. 67K, 67I and 83E). The workingprinciple relies on the formation of an ultrathin MoO_(x) layer on theMoS₂ surface with subsequent charge trapping/detrapping at theAg/MoO_(x) interface. Notably, no memory effect was observed for deviceswithout the oxide layer. See, Bessonov, A. A., et al., Layeredmemristive and memcapacitive switches for printable electronics. NatMater, 2015. 14(2): p. 199-204, which is incorporated by reference inits entirety. These memristors, written to various states during theirvirgin runs, demonstrate excellent retention over a period of 2 h (FIGS.83A-83E). By testing N=20 random devices of one fabricated batch, boththe threshold voltage and initial conductance only slightly depend onthe testing conditions: V_(th)=0.16±0.02 V, G_(m) ^(OFF)=13.4±4.0 nS onthe silicon; V_(th)=0.17±0.02 V, G_(m) ^(OFF)=18.4±8.4 nS for liftedoff; V_(th)=0.17±0.02 V, G_(m) ^(OFF)=14.4±6.9 nS for sprayed syncells(R_(m) ^(OFF)=1/G_(m) ^(OFF)). While similar behavior was observed formultiple devices during their virgin runs, performance of these devicesvaries for the next cycles (contrasting with the previously observedstable behavior in Bessonov et al. (2015)): This is probably associatedwith non-uniform scanning voltage rate applied during the experiments(FIG. 83C).

State Machine Operation

Once assembled together, the developed components form a state machine.To operate reliably, the microcircuit has to meet specific energy andpower requirements. The first one has already been briefly mentioned andsatisfied by the choice of the appropriate memristor: Generatedphotodetector voltage c has to exceed the threshold memristor voltageV_(th). The second criterion is that the memristor should not change itsstate if there is only an analyte. To this end, all devices were coveredexcept the chemiresistor with a hBN monolayer, ensuring that no chemicalreaction is happening with them (FIG. 73). Thirdly, the memristor shouldnot change its state if there is only light. This is achieved bydesigning the chemiresistor with the initial conductance G_(ch) ^(in),such that the voltage generated across the memristor does not exceedV_(th). This sets the lower limit for the initial chemiresistance(R_(ch) ^(in)=1/G_(ch) ^(in)), which can be determined by Ohm's law (seeSI for details):

$\begin{matrix}{{R_{ch}^{in} > {{R_{m}^{OFF}\left( {\frac{ɛ}{V_{th}} - 1} \right)} - R_{ph}}},} & (3)\end{matrix}$

where R_(ph) is the photodetector resistance. After the reaction withthe analyte, the chemiresistor decreases its resistance to R_(ch) ^(ƒ).This allows the memristor to change its state from R_(m) ^(OFF) to R_(m)^(ON), which again can be assessed through the Ohm's law:

$\begin{matrix}{R_{m}^{ON} = {\frac{R_{ch}^{f} + R_{ph}}{\frac{ɛ}{V_{th}} - 1}.}} & (4)\end{matrix}$

For memristor to change its state, the following has to be satisfied:R_(m) ^(ON)>R_(m) ^(OFF), yielding:

$\begin{matrix}{R_{ch}^{f} < {{R_{m}^{OFF}\left( {\frac{ɛ}{V_{th}} - 1} \right)} - {R_{ph}.}}} & (5)\end{matrix}$

Equations (3) and (5) set requirements for the circuit design. In caseof TEA, R_(ch) ^(ƒ) can maximally reach ≈R_(ch) ^(in)/2, so MoS2 sizeshould be carefully chosen to satisfy Eqs. (3) and (5).

To demonstrate state machine operations, syncells were fabricated withthree components assembled in one closed circuit (FIG. 66A) and testedthem both (i) as fabricated on the silicon substrate and (ii) sprayed inthe air. In a typical experiment, a portion of dispersed syncells ispipetted onto the silicon substrate and is left to dry until all waterevaporates naturally. Next, the initial syncell state was queried: usingprobe manipulators, both the memristor and the chemiresistorconductances were measured on N=100 syncells. The remainder of thesyncells is sprayed across in an enclosed tube; while on-the-substratesyncells are directly placed inside (FIGS. 74A-74E). The analyte iscontinuously sprayed using the second nebulizer from the top of the tubestarting 5 s before and ending right after the syncells are sprayedacross. Syncells are then left for 1-2 h inside to react with theanalyte and dry. Then syncells were placed under the microscope andilluminate every photodetector individually for 5 s (532 nm laser, 7μW/μm²). Next, the final state of N=100 syncells were assessed,repeating the same measurements as for the initial state. While forsprayed experiments these are random syncells, syncells are identifiedfor on-the-substrate experiments, extracting individual changes on everysyncell. Upon exposure to 10 mM TEA, sprayed syncells change theirchemiresistor conductance from G_(ch) ^(in)=8.9±3.1 nS to G_(ch)^(ƒ)=17.3±4.1 nS (in consistency with FIG. 67H), allowing memristorconductance change from G_(m) ^(OFF)=13.3±4.8 nS to G_(m) ^(ON)=17.3±8.9nS after laser illumination (FIG. 68A). Similar results were obtainedfor syncells on the substrate: Chemiresistor conductance changed fromG_(ch) ^(in)′=9.6±1.3 nS to G_(ch) ^(ƒ)=19.1±1.9 nS, enabling thememristor conductance change from G_(m) ^(OFF)=12.6±3.5 nS to G_(m)^(ON)=16.0±4.0 nS (FIG. 68C), having 41 syncells that did not changetheir memristor state (red circles in FIG. 68E). The latter can be dueto multiple reasons: power requirements are not met (ε/V_(th)<1), Eq.(5) is not satisfied, or component damage during the flight. Controlexperiments with light only showed that 6 syncells change the memorystate in the absence of the analyte, meaning that Eq. (3) was notsatisfied in their case (green triangles in FIG. 68E). Due to thelimited range of R_(ch) change, R_(m) changes are not statisticallysignificant. However, by tracking individual responses from syncells onthe substrate, successful state changes are identified in some syncells(FIGS. 68E and 84A-84C).

To further strengthen the demonstration, conductive carbon nanotube ink(0.2 g/l) was used as the analyte. For these experiments, the baresyncell substrate was used instead of MoS2 as the chemiresistor. SU-8 isan insulating material (sheet resistance ˜10 pS), and its lowconductance significantly strengthens condition of Eq. (3), whileadsorbed carbon nanotubes form a percolated network with conductivitieson the order of μS (FIGS. 85A-85C), providing high resistance modulationto satisfy Eq. (5). Control experiments with exposure of these syncellsto light-only demonstrate that no syncell changed its memristorconductance (FIG. 68D). In a typical experiment, sprayed syncells changetheir chemiresistor conductance from G_(ch) ^(in)′=8.7±2.0 pS to G_(ch)^(ƒ)=4.3±2.7 μS, inducing memristor change from G_(m) ^(OFF)=14.7±6.0 nSto G_(m) ^(ON=)0.47±0.44 μS, having 29 syncells that did not work (FIG.68B). For syncells on the substrate, chemiresistor conductance changedfrom G_(m) ^(OFF)=9.6±1.1 pS to G_(ch) ^(ƒ)=4.9±2.9 μS, inducingmemristor change from G_(m) ^(OFF)=12.9±3.9 nS to G_(m) ^(ON)=0.50±0.49μS (FIG. 68D), having 16 syncells that did not work (FIG. 68F). FIGS.68G-68H shows CSMs fabricated on the silicon substrate (FIG. 68G) andupon spraying in air within a confined chamber (FIG. 68H).

Demonstration of Constrained Environmental Sensing

Researchers have identified several important closed systems from whichit is difficult to extract information or interface electronics withinan inaccessible interior. See Lillesand, T., Kiefer, R. W. & Chipman, J.Remote Sensing and Image Interpretation. 1, 1-59 (2014), which isincorporated by reference in its entirety. Examples include oil and gasconduits, chemical and biosynthetic reactors, porous geologicalmaterials for upstream oil and mining exploration and the humandigestive tract. See Brunete, A., Hernando, M., Torres, J. E. & Gambao,E. Heterogeneous multi-configurable chained microrobot for theexploration of small cavities. Automat. Constr. 21, 184-198 (2012),Murvay, P.-S. & Silea, I. A survey on gas leak detection andlocalization techniques. J. Loss Prevent. Process Ind. 25, 966-973(2012), Rajtar, J. M. & Muthiah, R. Pipeline Leak Detection System forOil and Gas Flowlines. J. Manufact. Sci. Eng. 119, 105-109 (1997),Gavrilescu, M. & Tudose, R. Z. Residence time distribution of the liquidphase in a concentric-tube airlift reactor. Chem. Eng. Proces. 38,225-238 (1999), Kurt, S. K., Gelhausen, M. G. & Kockmann, N. AxialDispersion and Heat Transfer in a Milli/Microstructured Coiled FlowInverter for Narrow Residence Time Distribution at Laminar Flow. Chem.Eng. Tech. 38, 1122-1130 (2015), Tan, X., Sun, Z. & Akyildiz, I. F.Wireless Underground Sensor Networks: MI-based communication systems forunderground applications. IEEE 57, 74-87 (2015), and Yamate, T.,Fujisawa, G. & Ikegami, T. Optical Sensors for the Exploration of Oiland Gas. J. Lightwave Technol. 35, 3538-3545 (2017), each of which isincorporated by reference in its entirety. Several methods to probe suchsystems exist, but they are either indirect or very limited in theirapplicability. At the same time, fully autonomous electronic chips havebeen limited to the millimetre-range, which remains too large foraddressing the above applications. See Kalantar-Zadeh, K. et al. A humanpilot trial of ingestible electronic capsules capable of sensingdifferent gases in the gut. Nat. Electronics 1, 79-87 (2018), andCostello, B. P. J. d. L., Ledochowski, M. & Ratcliffe, N. M. Theimportance of methane breath testing: a review. J. Breath Res. 7, 024001(2013), each of which is incorporated by reference in its entirety. Tothis end, it was demonstrate that CSMs can be injected into a pipelinesystem, probe it, and then be successfully retrieved to deliver thecaptured information.

To illustrate, a model pipeline section was fabricated, into whichgaseous ammonia was injected. Ammonia is a highly toxic gas used as afertilizer in agriculture and as a refrigerant in the chemical industry.See Kalantar-Zadeh, K. et al. A human pilot trial of ingestibleelectronic capsules capable of sensing different gases in the gut. Nat.Electronics 1, 79-87 (2018), and Farra, R. et al. First-in-Human Testingof a Wirelessly Controlled Drug Delivery Microchip. Sci. Trans. Med.(2012), each of which is incorporated by reference in its entirety. Itis also one of the most dangerous compounds to be transported throughpipelines. See Timmer, B., Olthuis, W. & Berg, A. Ammonia sensors andtheir applications—a review. Sens. Actuat. B 107, 666-677 (2005), whichis incorporated by reference in its entirety. To probe the pipelineinternally, CSMs were first injected within the system (FIG. 99A) as anebulized aerosol. A valve is then used to pulse ammonia vapour (˜10kPa) into the system, allowing the CSMs to interact with it for 30 min.Next, the ammonia valve is closed and the CSMs are retrieved from thecollector (FIGS. 99B-99C). The experimental procedure is similar to theprevious section, with some CSMs inserted into the tube on-the-substrateas a control. Ammonia vapour acts as an n-dopant for the MoS₂ layer (seeNielsen, A. Ammonia: Catalysis and Manufacture (ed Anders Nielsen)329-346 (Springer Berlin Heidelberg, 1995), which is incorporated byreference in its entirety), changing MoS₂ conductances from G_(ch)^(in)=9.1±2.2 nS to G_(ch) ^(ƒ)=18.5±2.5 nS for the sprayed CSMs and,consequently, allowing memristor conductance change from G_(m)^(OFF)=12.5±3.9 nS to G_(m) ^(ON)=14.5±4.3 nS after laser illumination(two-tailed p-value equals 0.0007, N=100, FIG. 99D) with similar resultsfor the on-substrate CSMs (FIGS. 99E, 99F and 101A-101C).

State Machines for Soot Exposure Monitoring

Soot nanoparticles emitted by diesel engines, industrial emissions, andpower plants pose health, climate, and environmental risks. See Cho, B.et al. Charge-transfer-based Gas Sensing Using Atomic-layer MoS₂ . Sci.Rep. 5, 8052 (2015), which is incorporated by reference in its entirety.Aerosolized micro- and nanoparticles can travel thousands of kilometresbefore sedimentation (see Bernstein, J. A. et al. Health effects of airpollution. J. Allergy Clin. Imm. 114, 1116-1123 (2004), which isincorporated by reference in its entirety), making it challenging topredict soot distribution and impact. To date, the large area monitoringof soot remains an economically inviable task. To this end, CSMs asdispersed, printed devices can potentially cover large areas tosuccessfully detect soot, remaining virtually invisible to the nakedeye, but otherwise easily detectable on a surface (see below). In thiscase, aerosolization allows CSMs to be rapidly printed over a specificarea of interest as intact, functional, autonomously powered devices.

To demonstrate the monitoring of undesirable particulates from surfacedispersed CSMs, the nebulized CSMs were deposited over an area of0.6×0.6 m². Next, 2 g/l of Printex XE2-B soot was loaded into a separatenebulizer and sprayed over three distinct locations (FIGS. 100A, 100Band 102A-102B), simulating localized particulate efflux. For theseexperiments, an insulating substrate (SU-8, sheet resistance ˜10 pS)instead of the MoS₂ was used as the CSM chemiresistor. The remainder ofthe experimental procedure is similar to previous experiments. By theirnature, soot particles are highly conductive (see Derbyshire, E. NaturalMinerogenic Dust and Human Health. AMBIO 36, 73-77 (2007), which isincorporated by reference in its entirety); thus, the chemiresistorelement drastically changes its conductance from G_(ch) ^(in)=7.4±2.4 pSto G_(ch) ^(ƒ)=0.80±0.26 μS upon exposure to soot. This furthertranslates into memristor conductance changes from G_(m) ^(OFF)=13.7±4.2nS to G_(m) ^(ON)=127±72 nS upon laser illumination (FIG. 100D). Theretrieved CSM positions allow determination of the exposed and unexposedareas (FIG. 100C).

Enhancements of State Machines to Aid Standoff Detection

To efficiently detect the location of CSMs at standoff distances, adistinct batch was fabricated, where the CSM base consisted of aretroreflector design. The design follows that of Switkes et al. as 100μm-size retroreflector for low intensity laser (10 mW/cm²) reflectedlight from distances of up to 1 km. See Grob, B., Schmid, J., Ivleva, N.P. & Niessner, R. Conductivity for Soot Sensing: Possibilities andLimitations. Anal. Chem. 84, 3586-3592 (2012), and Switkes, M., Ervin,B. L., Kingsborough, R. P., Rothschild, M. & Sworin, M. Retroreflectorsfor remote readout of colorimetric sensors. Sens. Actuat. B 160,1244-1249 (2011), each of which is incorporated by reference in itsentirety. CSM retroreflectors were fabricated using SU-8 coated with 100nm Ag designed in the checkered shape that allows them to reflect lightback to the source from angles up to 60° (FIG. 69B). A customlaser-scanning system (FIG. 69A) was used to rapidly scan (<1 ms) anddetect reflection from the CSMs that landed after spraying over an 8×8mm² area at a 5 cm standoff distance (FIG. 69C). Careful examinationunder the microscope showed that N=34 CSMs were detected (FIGS. 69D and69E): 25 CSMs (100% refers to the percentage of CSMs detected by laserscanning versus the total number of CSMs identified under the microscopefor a given category) that had their reflectors facing up and N=9 (56%)that were flipped. The yield becomes slightly lower for CSM detection onthe inclined substrate due to the imperfect backreflections (FIGS.69F-69H): 23 CSMs (82%) were facing up and 7 CSMs (32%) that wereflipped. These results suggest that this attribute of CSMs can aid intheir tracking and recovery over large areas, and with refinements,could increase the detection threshold to 100% with a 10 cm²/s scan.

The capability of grafting autonomous electronic circuits are capable oflogical operation and information storage onto sub-millimetre-sizedparticles, forming what is termed Colloidal State Machines (CSMs). Theseparticles can undergo aerosolization while carrying functionalelectronics on-board capable of interaction with the environment. With athickness of 1.24 μm and weight of ˜1.4 g/m², this CSM design representsone of the thinnest and lightest circuits produced to date. See Switkes,M., Ervin, B. L., Kingsborough, R. P., Rothschild, M. & Sworin, M.Retroreflectors for remote readout of colorimetric sensors. Sens.Actuat. B 160, 1244-1249 (2011), which is incorporated by reference inits entirety. In this design, the on-board circuit forms a state machinewith two inputs (chemical and optical) and one output comprised of amemristor. Owing to the usage of 2D materials, CSM requires only 30 nWto irreversibly record events, granting it the ability to be poweredfrom the energy harvested by the on-board 2D photodiode (30-100 nW). Theresults of chemical sensing are irreversibly stored in the memory(inducing memristor conductivity changes of up to 150 times).Furthermore, the addition of integrated retroreflectors allows thedispersed CSMs to be rapidly (<1 ms/frame) detected by a laser-scanningsystem. Colloidal state machines may find applications in a wide rangeof areas, including biosensing (e.g., within the human digestive tract),large-area sensing, confined space monitoring (e.g., chemical andbiosynthetic reactors, oil and gas conduits), and aerospace programs.

Electronic Power Requirements

Batteries typically have 0.1 nW/μm³ with energy capacities of 1 nJ/μm.See Spellings, M. et al. Shape control and compartmentalization inactive colloidal cells. Proceedings of the National Academy of Sciences112, E4642-E4650 (2015), and Ferrari, S. et al. Latest advances in themanufacturing of 3D rechargeable lithium microbatteries. Journal ofPower Sources 286, 25-46 (2015), each of which is incorporated byreference in its entirety. Basic electronic devices, like a quartzoscillator and a radio frequency identification (RFID) tag made fromconventional III-V electronics, consume approximately 100 nW and 10 μW,respectively. A sub-millimeter battery with 100×100×100 μm³ dimensionsshould provide a power of 100 μW and store energy of 1 mJ, which isenough to power the above mentioned devices for 165 min and 100 sec,respectively. To ensure longer operational times, early attempts atautonomous microsystems often rely on external energy harvesting. Inparticular, some versions of smart dust harvested energy from wirelesselectromagnetic radiation, limiting the device operation to a distanceof just a few meters. See Seo, D. et al. Wireless Recording in thePeripheral Nervous System with Ultrasonic Neural Dust. Neuron 91,529-539 (2016), which is incorporated by reference in its entirety.Unfortunately, this approach does not appear capable of downwardscaling, due to receiver size limitations. See Seo, D., Carmena, J. M.,Rabaey, J. M., Maharbiz, M. M. & Alon, E. Model validation ofuntethered, ultrasonic neural dust motes for cortical recording. Journalof Neuroscience Methods 244, 114-122 (2015), which is incorporated byreference in its entirety. Alternative energy harvesting techniques,such as chemical power harvesting, bacteria-produced power, ultrasound,magnetic field and light, are continuously being developed. See Zebda,A. et al. Single Glucose Biofuel Cells Implanted in Rats PowerElectronic Devices. Scientific Reports 3, 1516 (2013), Kim, H. & Kim, M.J. Electric Field Control of Bacteria-Powered Microrobots Using a StaticObstacle Avoidance Algorithm. IEEE Transactions on Robotics 32, 125-137(2016), Servant, A., Qiu, F., Mazza, M., Kostarelos, K. & Nelson, B. J.Controlled In Vivo Swimming of a Swarm of Bacteria-Like MicroroboticFlagella. Advanced Materials 27, 2981-2988 (2015), and Chang, S. T.,Paunov, V. N., Petsev, D. N. & Velev, O. D. Remotely poweredself-propelling particles and micropumps based on miniature diodes. NatMater 6, 235-240 (2007), each of which is incorporated by reference inits entirety. They deliver between 0.1 and 10 nW/(100×100 μm²) of power,which to date is not enough for conventional electronic needs.Fortunately, 2D material devices are predicted to bypass thesedifficulties, having a number of advantages, such as low-powerperformance as compared to Si (<0.5 V), acceptable gate control withsubthreshold swings <<60 mV/dec, and large turn on currents (>10³μA/μm). See Ionescu, A. M. & Riel, H. Tunnel field-effect transistors asenergy-efficient electronic switches. Nature 479, 329-337 (2011), andFiori, G. et al. Electronics based on two-dimensional materials. NatNano 9, 768-779 (2014), each of which is incorporated by reference inits entirety. Most recent publications focus on individual 2D devices,while no integration of power harvesting and usage has been demonstratedyet. See Wang, Q. H., Kalantar-Zadeh, K., Kis, A., Coleman, J. N. &Strano, M. S. Electronics and optoelectronics of two-dimensionaltransition metal dichalcogenides. Nat Nano 7, 699-712 (2012),Radisavljevic B, Radenovic A, Brivio J, Giacometti V & Kis A.Single-layer MoS₂ transistors. Nat Nano 6, 147-150 (2011),Lopez-Sanchez, O., Lembke, D., Kayci, M., Radenovic, A. & Kis, A.Ultrasensitive photodetectors based on monolayer MoS2. Nat Nano 8,497-501 (2013), Cheng, R. et al. Electroluminescence and PhotocurrentGeneration from Atomically Sharp WSe₂/MoS₂ Heterojunction p-n Diodes.Nano Letters 14, 5590-5597 (2014), and Lopez-Sanchez, O. et al. LightGeneration and Harvesting in a van der Waals Heterostructure. ACS Nano8, 3042-3048 (2014), each of which is incorporated by reference in itsentirety. Moreover, these efforts tend to describe 2D devices on flatsilicon wafers, while their performance on substrates of high curvatureis less understood.

EXAMPLES Syncell Fabrication Process (1). Chemical Vapor Deposition(CVD) Growth of Graphene (G), MoS₂ and Hexagonal Boron Nitride

CVD graphene sheets were produced as follows: briefly, copper foil (AlfaAesar, 99.8%, 25 μm thick, for graphene growth) with a size of 2.0×2.2cm was used as substrate, the copper was annealed at 30 sccm H₂ gas flow(˜560 mTorr) for 30 min at 1000° C. and then 0.5 sccm (for single layergraphene) or 10 sccm (for bilayer graphene. See Tu Z, Liu Z, Li Y, YangF, Zhang L, Zhao Z, et al. Controllable growth of 1-7 layers of grapheneby chemical vapour deposition. Carbon 2014, 73: 252-258, which isincorporated by reference in its entirety.) methane was introduced for15 min or 10 min, respectively. After that, the furnace was kept at1000° C. for another 5 min and turned off. Cu foil was cooled down andremoved out at room temperature.

(2). Chemical Vapor Deposition (CVD) Growth of MoS₂

Sapphire or SiO₂ substrate (7.0 cm×1.7 cm) washed with acetone (5 min)and isopropyl alcohol (IPA, 5 min) was used in the growth of MoS₂, MoCl₅powders (Sigma Aldrich, 99.99%, ˜4 mg) was loaded onto a SiO₂/Sisubstrate and placed in the central part of the heating zone, the sulfurpowder (Sigma Aldrich, 99.998%, ˜0.5 g) was added in a separate Al₂O₃boat and placed at the upper stream side of the tube where thetemperature was about 200° C. during the reaction. The sapphire or SiO₂substrate was placed at the downstream side 1 cm next to MoCl₅. The tubewas purged with 50-sccm Ar under vacuum for 30 min, then the furnace washeat to 850° C. in 30 min. The Ar flow kept at 50 sccm and the displayedpressure was about 1.13 torr. The tube was kept at the same temperaturefor another 10 min and then cooled down to room temperature naturally.

(3). Liquid Exfoliation of the Black Phosphorus and Other Nanoparticlesfor Ink Application

60 mg of Black phosphorus was well grounded before being dispersed in 20mL EG and a tip sonicator (10% maximum power) was used to sonicate theresulted mixture for 10 hours with liquid cooling at 4° C. The obtainedsolution was centrifuged at 2000 rpm at room temperature for 20 min toproduce the final dispersion of BP nanoflakes. To determine theconcentration of BP nanoflakes, we sampled 1.5 g solution and filteredit using a 0.2 μm-sized PTFE syringe filter, and weighted the BPnanoflakes left on the filter after drying under vacuum overnight. Thedispersion was diluted to solutions with different concentrations tocollect the UV-Vis absorption. The spin coating was used to preparesamples of BP nanoflakes on SiO₂/Si (or gold-coated) substrate for AFM,Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Adroplet of the dispersion was added on to a Holy-carbon grid and driedunder vacuum to prepare the specimen for TEM.

For other 2D nanoflakes or nanoparticles, single layer graphene oxidedispersion in water (500 mg/L), molybdenum disulfide (MoS₂) pristineflakes in solution (1-8 monolayers, 18 mg/L), and MoS₂ ultrafine powder(˜90 nm) were purchased from Graphene Supermarket and used as received.Ethylene glycol (Sigma Aldrich, 99.8%) was used to further disperse MoS₂ultrafine powder for the ink application.

(4). Noncovalent Functionalization of CVD Graphene on Copper (GrapheneA)

A procedure reported in literature was adopted for the noncovalentfunctionalization via π-π stacking. Generally, the copper foil withgraphene (single layer or bilayer) and a size of 2.0×2.2 cm wasincubated in the dimethyl formamide (DMF) solution of functionalmolecules for 1 h and washed with fresh DMF, ethanol, and dried at roomtemperature (the washing step can remove those excess molecules whichwere not attached to the graphene surface). Specifically, 2 mL DMFsolution of 1-pyrenebutyric acid (97%, Sigma Aldrich), 1-aminopyrene(97%, Sigma Aldrich), 1,5-diaminonaphthalene (97%, Sigma Aldrich), orother functional molecules (2 mmol/L) was added into a 10 mL-beaker withcopper foil, and mechanically shaken for 1 h, then the copper foil wasremoved out and rinsed with DMF and ethanol in sequence, with each of 30s. After drying, the copper foil was spin-coated with a PMMA layeraround 230 nm using 950PMMA A4 (MicroChem) at 3000 rpm for 1 min. Thecopper layer was etched out with ammonium persulfate (APS-100, TRANSENECO INC) and the left graphene/PMMA film was rinsed with deionized water.For characterization, the film was transferred onto Si/SiO₂ substratewith the graphene side down and characterized with Raman spectroscopywith or without washing out the PMMA layer using acetone, to comparewith the pristine graphene. For further fabrication and modification,the film was picked up with Si/SiO₂ substrate with the graphene side upor a polydimethylsiloxane (PDMS) stamp (2.5×2.5 cm, 2 mm thickness) hasbeen attached to the graphene/PMMA layer before the etching step.

(5). Noncovalent Functionalization of Graphene (Graphene A) on PMMA Film

In this step, methanol, a poor solvent of PMMA, was used as the onlysolvent to prepare the solution of functional molecules or rinse in thisstep. Functional molecules like 1-pyrenebutyric acidN-hydroxysuccinimide ester (95%, Sigma Aldrich) (4 mmol/L) and1,5-diaminonaphthalene were used in this step (a heating to 80° C. isrequired to dissolve like 1-pyrenebutyric acid N-hydroxysuccinimideester in methanol). A few drops of the solution were added to overcoverthe surface of the SiO₂ wafer or PDMS-supported PMMA/graphene film andthe incubation time is 15 min. After that, the film was rinsed withfresh methanol for 30 s to remove any residual functional moleculeswhich were not attached to the graphene surface. After drying, the filmis ready for the ink-jet printing in the next step. The SiO₂-supportedfilm can be characterized with Raman spectroscopy, while thePDMS-supported film can be transferred to another piece of Si/SiO₂ waferfor characterization via washing out the PMMA layer.

(6). Ink-Jet Printing of Polymer Latexes or their Composite Solutionwith Nanoparticles

Polymer latex, polystyrene (PS) latex (Sigma Aldrich, amine-modifiedpolystyrene, fluorescent orange, 0.1 μm mean particle size, 2.5 wt %)for example, were diluted with ethylene glycol (EG) to 1.25%(vol:vol=1:1), 0.83% (1:2), 0.50% (1:4), and 0.25% (1:9) as inks for theprinting. The PS latex was also composting with zinc oxide (ZnO)nanoparticle ink (2.5 wt. %, viscosity 10 cP, work function −4.3 eV,Sigma Aldrich) and further diluted with EG (vol:vol:vol=2:1:1), ironoxide(II,III), magnetic nanoparticles solution (10 nm avg. part. size, 5mg/mL in H₂O, Sigma Aldrich) and further dilute with EG(vol:vol:vol=9:2: 7), or exfoliated black phosphorus solution(vol:vol=1:1) to prepare functional inks for the printing. In the inkjetprinting at room temperature using a MICROSYS printer, from CartesianTechnologies, a ceramic printer needle was used and the printed inkvolume is 1 nL for each dot, the spacing between the two adjacent dotsis 500 μm, and the printing area is typically 1.5-2.0 cm in length andwidth. After printing, the ink was dried at room temperature overnightand further under house vacuum for 1 h. This Si/SiO₂ or PDMS-supportedgraphene/PMMA film with the printed dot array was annealed at 120° C.for 10 min and cooled down to room temperature, and ready for thenext-step use. A printer from Fujifilm Dimatrix Materials (PrinterDMP-2850) was also used and n ink volume of 10 pL or 1 pL was printed toprepare smaller-sized microspot with PS latex ink (1.2 wt %, 50 nm meanparticle size, in a mixture of water and ethylene glycol (1:1)).

For the printing of conductive silver microspot array, silver dispersion(nanoparticle, 30-35 wt. % for printing on plastic films, Sigma-Aldrich)was diluted with ethylene glycol/water mixture (1:1 in volume) for 200times as nanoink and the MICROSYS printer for the printing, with aprinting volume of 1 nL. In addition to the use of printers above toprint the microparticles, the contact printing was done with a capillarytube with an ink volume around 0.5 μL by hand, with this, larger spotswere printed with a diameter about 1 mm. The sequential printing ofsilver microspot array and capillary contact printing allow users toprint polymer or its composite particles with separated silver spots. Asa simple demonstration, the silver microspot array was first printedwith an ink volume of 1 nL for each spot a space of 500 μm for the twoadjacent dots, and annealed at 120° C. for 10 mins. The polymer or itscomposite spots were printed by capillary contacting to cover the silverarray, further annealing at 130° C. for 10 mins is applied to enhancethe bonding between the two materials.

(7). The Preparation of the Second Piece of Graphene/PMMA Film (GrapheneB)

To prepare the second piece of graphene/PMMA film (which will be used asthe cover layer during the stacking process), a modified fabricationprocedure was adopted. Particularly, one-side functionalizedgraphene/PMMA film in step 4 was transferred onto a relatively largerSi/SiO2 wafer (5×5 cm), and drops of the functional molecule (i.e.,1-pyrenebutyric acid N-hydroxysuccinimide ester, 1,5-diaminonaphthalene)solution in methanol were added onto the wafer until the completeinfusion of the solution into the underlying surface of thegraphene/PMMA film. The film was incubated for 10 mins and after that,washed with fresh methanol, transferred back to the deionized water, andrinsed with water for 4 times with 10 mins each time. This film was leftin water and ready for the next step.

(8). Stacking, Liftoff, and Auto Perforation

The annealed graphene/PMMA film on SiO₂ or PDMS substrate in Step 7severing as the bottom layer to pick up the cover layer in Step 5 fromwater. The two films with the sandwiched PS or its nanocomposite dotswere dried at room temperature for 1 h and then annealed at 120° C. for15 mins. After that, the films together with the substrate were placedinto a 50-mL beaker with a magnetic stir bar, 10-15 mL of ethanol/water(4:1 in volume) was added, the beaker was sealed with paraffin andheated to 80° C. under stirring for 10 mins, after that, the solutionwas cooled down to room temperature and water for 12 h, with visible,dark particles suspending in the solution. After standing overnight,these particles were settled down and the solution was replaced withfresh ethanol/water (4:1). The heating, stirring, settling, and solutionreplacement procedure was repeated another two time to remove anyresidual PMMA in the solution or on the graphene surface and after that,these particles were stored in the solution and fishing out on to glassslide, SiO₂ substrate, or ITO-coated glass via pipette for furthercharacterization or measurement.

(9). The Preparation of 2D Syncell Particles with CVD Graphene withoutFunctionalization

The preparation of syncell particles with pristine graphene as outerlayer is simpler and faster than the above procedure to prepare thesyncell particles with two-side functionalized graphene. Briefly,graphene (A) was transferred onto PMMA with either PDMS or Si/SiO₂ assubstrate, the film with graphene layer up. The film was printed with PSor PS/nanoparticles dot array, and annealed at 120° C. for 10 mins. Theother layer of graphene (B layer) was transferred to PMMA. This film wasfloated in water and stacked onto graphene A to form the sandwich. Thestacked two graphene/polymer films with PS dots (or PS nanocompositedots) dried at room temperature overnight and then annealed at 120° C.for 10 mins. The further liftoff operation was the same as above.

(10). The Preparation of 2D Syncell Particles with Molybdenum Disulfide(MoS₂) and Hexagonal Boron Nitride hBN (Syncell)

The preparation procedure is similar that in (9). The only difference isthe transfer of MoS₂ sheet. MoS₂ grown on Si/SiO₂ substrate wasspin-coated with a thin PMMA layer (same as above) and the MoS₂/PMMAfilm was liftoff from the SiO₂ substrate with KOH solution (2 M inwater) as etchant at 80° C. The film was rinsed with deionized water 5times and used for the further printing, stacking, and liftoff, toprepare MoS₂ syncell. For hBN syncell, single layer or multi-layer hBNfilm grown on grown on copper foil produced by CVD method was purchasedfrom Graphene Supermarket, the transfer and further preparation ofsyncell particles are the same as that of the graphene syncell particlesabove.

(11). Characterization and Measurement

The optical images of microparticles were acquired from ZEISS Axio ScopeAl with a magnification of 5 and 20 times. The visualization of theliftoff process was also monitored the same microscope. A temperaturecontrolled microscopic stage from Linkam Scientific was coupled to themicroscope system for heating up solution during the liftoff. Ramanspectroscopy was performed on a Horiba Jobin Yvon LabRAM HR800 systemusing a 532 nm excitation laser, 10× objective lens with ˜10 μm diameterspot size, and 1800 lines/mm grating. The profile data of themicroparticles were obtained with Tencor P-16 Surface Profilometer™using a 2 um radius diamond tipped stylus Step height, with ameasurement range of 20 Angstroms to 1 mm. Static water contact anglewas measured by ramé-hart Model 590 goniometer. The transmittance of BPsolution was measured with Shimadzu UV-3101PC Spectrophotometer at awavelength of 660 and 1176 nm. Freshly exfoliated BP solution was usedas a stock solution and dilute at different times for the measurement.NanoSight LM10 (Malvern) was used for the rapid and accurate analysis ofthe size distribution and population of BP nanoparticles from 10 nm to2000 nm in diameter using single particle tracking.

Atomic force microscopy (AFM) was performed using Asylum MFP-3D-BIO intapping/AC mode with Si tips (Asylum, AC240TS). The scan rate was 0.7Hz, and scan angle was set to be 0°. Black phosphorus (BP) samples wasprepared via spin-coating onto a plasma-treated SiO₂/Si substrate.Scanning electron microscope was conducted on Zeiss MerlinHigh-resolution SEM, which is equipped with an in-lens energy selectivebackscatter detectors for back-scattered electron imaging and thevisualization of regions of different composition. For SEM observation,the BP/PS composite sample was prepared via mixing of 100 μL of PS latexnanoparticle dispersion (2.5 wt %) and 100 μL of BP dispersion inethylene glycol (0.25 mg/mL) and drying on the hot plate of 120° C. for10 min. Transmission Electron Microscopes (TEM) of BP nanoflakes wascarried on JEOL 2010 Advanced High-Performance TEM, and BP nanoflakeswere suspended on a holy-carbon grid for the characterization. For thefluorescence imaging of MoS₂ or graphene microparticles, the particlestogether with solvent were sampled and naturally dried on glass slides,a broadband supercontinuum white light source (NKT Photonics, SuperKEXTREME EXR-15) was attenuated with a neutral density filter.Fluorescence signal was filtered with band-pass filters and collected ona 512×512-pixel imaging area of electron multiplying charge coupleddevice (EMCCD) camera (Andor, iXon3). X-ray photoelectron microscopy(XPS, Kratos AXIS Ultra spectrometer with a monochromatized Al Kαsource) was used to analyze the surface chemistry and compositions ofvarious samples including microparticles with different 2D materials,functionalized graphene, BP nanoflakes, and others.

To study the electrical properties of microparticles with the probestation, a MATLAB code was written to execute commands over asemiconductor parameter analyzer (SPA) (Agilent E5262A Source MeasureUnits), which is used to query electrical information of themicroparticles aided by a probe station. The microparticles were loadedinto a probe station chamber, and the electrical measurements werecarried out in an ambient environment at room temperature with sweepingvoltage rate was 50-100 mV/s. In general, the electrical properties ofthese graphene microparticles can be categorized into two major modes:in-plane mode and vertical (out-of-plane) mode. In the in-plane mode,the microparticles are placed onto an insulating surface (typicallyglass) with one of the 2D material (typically graphene) surfaces facingup, and the Tungsten (W) probe head gently placed on the materialsurface. To aid the process of locating a microparticle under themicroscope atop the probe station, its location is separately locatedunder an optical lens and marked before it was placed in the probestation. In the vertical mode, vertical conductivities (or through-planeconductivity of the 2D material-composite vertical stack, i.e.Gr-PS/BP-Gr) are typically tested. In this case, a conductive substratefor the microparticle is needed to complete the probe-particle-substratecircuit. ITO substrate was selected for its robustness.

Syncell as an Aerosolizable Electronics

1. Fabrication

To define polymer syncell bases, the first photolithography step wasperformed using the negative photoresist SU-8 2002 on SiO₂/Si wafer(FIGS. 72A-72C). Next, a monolayer of MoS₂ (patterned in 25 μm widestripes using oxygen etching) with a PMMA support layer was transferredonto the structure with subsequent annealing at 80° C. for 1 h and 150°C. for 30 min. The wafer was then washed in acetone and ethanol anddried under nitrogen to remove the PMMA layer. In parallel, a monolayerof WSe₂ was prepared on a separate wafer: 25 μm wide WSe₂ stripes weredefined using the second photolithography step with the positivephotoresist Shipley 51805 and subsequent oxygen etching. The photoresistwas removed in RemoverPG developer. The patterned WSe₂ monolayer wasthen transferred onto MoS2 using PMMA as the support layer, annealed at80° C. for 1 h and 150° C. for 30 min. The wafer was washed in acetoneand ethanol and dried under nitrogen. The third photolithography with aLOR30B sacrificial layer and a positive photoresist Shipley S1805 wasused to define 40 nm-thick gold electrical contacts, which weredeposited using a Denton E-beam evaporator. The lift off process wasperformed in Remover PG at 80° C.

The fourth photolithography step with a LOR30B sacrificial layer andShipley S1805 was used to define the structure of subsequent MoS₂ film.The MoS₂ film was deposited using a modified Langmuir-Blodgett method,where the MoS₂ film was collected at an ethanol-hexane interface. See,Bessonov, A. A., et al., Layered memristive and memcapacitive switchesfor printable electronics. Nat Mater, 2015. 14(2): p. 199-204, which isincorporated by reference in its entirety. To form the top oxide layer,the structure was annealed at 200° C. for 2 h. The lift off process wasperformed in Remover PG at 80° C. The fifth photolithography with aLOR30B sacrificial layer and Shipley S1805 was used to define 100nm-thick silver electrical contacts. The lift off process was performedin Remover PG at 80° C. A monolayer hBN (patterned in 50 μm widestripes) was then transferred on top. Since hBN is transparent, itsalignment on the syncell is very challenging. To this end, hBN wastransferred with S1850 photoresist in order to help visualize thestructure (the photoresist was removed afterwards). Finally, syncellswere coated with a PMMA layer for support and lifted off the substrateusing KOH solution. To disperse syncells, the PMMA was dissolved inacetone.

Retroreflectors were fabricated using SU-8 photolithography withsubsequent evaporation of 100 nm silver.

2. Methods

2D Materials.

Large-area MoS₂ films were grown by a chemical vapor deposition (CVD)process described elsewhere. See, Yu, Y., et al., Controlled ScalableSynthesis of Uniform, High-Quality Monolayer and Few-layer MoS2 Films.Scientific Reports, 2013. 3: p. 1866, which is incorporated by referencein its entirety. Briefly, solid 0.5 g S and 4 mg MoCl₅ were used asprecursors, and a 2×1 cm² 300 nm SiO2/Si wafer piece was used as agrowth substrate in a vacuum tube quartz furnace. The system was filledwith 50 sccm Ar for 1 h with subsequent growth at 850° C. under 2 Torrpressure for 10 min and a 30 min temperature ramp. As-grown MoS2 filmswere coated with polystyrene and peeled from the substrate—takingadvantage of the surface-energy-assisted method. See, Gurarslan, A., etal., Surface-Energy-Assisted Perfect Transfer of Centimeter-ScaleMonolayer and Few-Layer MoS2 Films onto Arbitrary Substrates. ACS Nano,2014. 8(11): p. 11522-11528, which is incorporated by reference in itsentirety. Continuous films of hBN and WSe₂ monolayers were purchasedfrom Graphene Supermarket and 6Carbon, respectively.

Characterization.

Raman and photoluminescence measurements were performed using a Ramanspectrometer HR-800 (Horiba BY) with 532 nm laser. Height profiles weremeasured using a CCi HD optical profiler. Electrical resistancemeasurements were performed in the ARS PSF-10-1-4 Cryogenic ProbeStation using micromanipulators as probes (7×, Micromanipulator).Conductance measurements were performed by scanning the voltage from−0.1 to 0.1 V.

Aerosol Experiments.

All aerosol experiments were performed with a Master Airbrush G22nebulizer in a closed tube in the laminar flow hood. Syncells (dispersedin 80% water/20% ethanol) were sprayed under 2-15 psi pressure from a300 μm nozzle. The second nebulizer was used to spray analyte dropletsin the orthogonal direction (FIGS. 74A-74E). Aggregated syncells,syncells with visual defects, and syncells that landed upside down wereexcluded from analysis.

Standoff Detection.

Standoff syncell detection was performed using a setup with galvanizedmirrors, a 532 nm laser, and a photodetector (H10330a-25,HAMAMATSU).

3. In-Flight Analysis

To further understand syncell in-flight behavior, rigorous mathematicalcalculations were performed on different aerosol aspects. The nebulizerprovides 2-15 psi pressure over a 2 cm long tube with a diameter of 0.3mm. This impulse provides initial droplet speeds of 7-100 m/s, which arerapidly slowed down due to the air drag. Time until the full stop in thehorizontal direction is called relaxation time and can be calculatedfrom the equation of motion:

$\begin{matrix}{{\frac{dv}{dt} = {{- \frac{3\rho_{air}}{4\rho_{particle}D}}v^{2}C_{d}}},} & (6)\end{matrix}$

where ν is the particle speed, ρ_(air) is the air density, ρ_(particle)particle density, C_(d) drag coefficient and D the particlecharacteristic length. Travelled distance in the horizontal directioncan be calculated by integrating the solution to Eq. (6). As will beshown in the following, drying time is much longer than the relaxationtime; therefore, the particle can be treated as being a liquid dropletfor relaxation calculations.

Droplets with 100-300 μm have relaxation times on the order ofmicroseconds, with higher speeds increasing particle drag and,consequently, shortening relaxation time (FIG. 77A). As expected,smaller droplets have smaller inertia, losing their speed more rapidlythan larger ones. This leads to longer travelled distance that increasewith initial droplet speed (FIG. 77C). Interestingly, droplets with 100μm diameter travel less than 0.3 m even with initial speed as high as1000 m/s.

The drying process consists of two distinct parts. While evaporating,the droplet loses energy at the expense of its temperature. This happensuntil it reaches an equilibrium temperature where convective heat fluxfrom the surroundings matches to energy lost due to evaporation. Thetime that it takes for the droplet to stabilize its temperature iscalled the cooling time. In the second part, the droplet temperature isstable while the diameter decreases. The time required for completedroplet evaporation is called the lifetime.

Cooling time can be calculated from a droplet energy balance (seeHolterman, H. J., Kinetics and Evaporation of Water Drops in Air, inInstitute of Agricultural and Environmental Engendering. 2003, which isincorporated by reference in its entirety):

$\begin{matrix}{{\tau_{c} = {- \frac{c_{p}D^{2}}{3h\; {\xi \left( {1 + {b\sqrt{Dv}}} \right)}\left( {\frac{{dp}_{sat}}{dT} + \gamma} \right)}}},} & (7)\end{matrix}$

where c_(p) is the specific heat (water: c_(p)=4180 J kg⁻¹ K⁻¹), h isthe heat of evaporation (water: h=22.6 10⁵ J/kg), b and ξ are specialparameters (see below), p_(sat) is the saturated vapor pressure, and γis a constant (˜67 Pa/K).

After the droplet temperature stabilizes, its diameter change can beapproximated as in Holterman (2003):

$\begin{matrix}{{\frac{dD}{dt} = {{- \frac{4M_{L}D_{vapor}}{D\; \rho_{particle}{RT}}}{\gamma \left( {T - T_{w}} \right)}\left( {1 + {0.276{Re}^{1\text{/}2}{Sc}^{1\text{/}3}}} \right)}},} & (8)\end{matrix}$

where M_(L) is the molecular weight of the evaporating liquid (water:0.018 kg/mole), D_(vapor) is the average diffusion coefficient for vapormolecules in the saturated film around the drop, T is the averageabsolute temperature, T_(w) is the wet-bulb temperature (ΔT=T−T_(w)), Reis Reynold's number, Sc is Schmidt's number, and R is the gas constant(8.31 J mol⁻¹ K⁻¹). Solving this yields the expression for the dropletlifetime:

$\begin{matrix}{{t_{life} = {\frac{2}{q_{0}q_{1}^{2}\Delta \; T}\left( {{q_{1}D_{0}} - {\ln \left( {1 + {q_{1}D_{0}}} \right)}} \right)}},} & (9)\end{matrix}$

where q₀ and q₁ are parameters defined later in the text.

Numerical calculations showed that cooling time decreases with dropletspeed, as vapor pressure decreases with speed, leading to fasterevaporation and cooling. Interestingly, the droplet stops much fastercompared to the cooling time (FIG. 77D). After its stop, the dropletstarts to slowly sediment, cooling down for 0.01-0.1 sec (at 17° C., 100μm droplet cools down by 4° C.). Finally, the droplet fully evaporatesafter 100-1000 sec of flight. Droplet lifetimes can be longer whenmultiple droplets coexist, increasing outer vapor pressure andconsequently decreasing evaporation rate, such as what occurs in clouds.

Sedimentation speed is calculated from the equilibrium condition, wherethe drag on a particle is equal to the buoyant force F_(B):

F _(B)=−½ρ_(air) AC _(d)ν².  (10)

For spherical objects under low Reynold's numbers, calculation followsthe famous Stokes' law. However, dried syncell has a non-spherical shapeand can possibly move into a non-Stokes regime. To account for this, thedrag coefficient needs to be modified.

Correction factors were introduced for non-spherical particles. In theStokes regime, the syncell will preferentially fall with the dragparallel to the axis of symmetry (α is aspect ratio) (see, Byron, M. L.,The rotation and translation of non-spherical particles in homogeneousisotropic turbulence. arXiv:1506.00478, 2015, which is incorporated byreference in its entirety):

$\begin{matrix}{{f = {- \frac{\left( \frac{4}{3} \right){\alpha^{- \frac{1}{3}}\left( {1 - \alpha^{2}} \right)}}{\alpha + \frac{\left( {1 - {2\alpha^{2}}} \right)\cos^{- 1}\alpha}{\sqrt{1 - \alpha^{2}}}}}},} & (11)\end{matrix}$

while in the non-linear regime, the syncell will rotate—having thefollowing ƒ:

$\begin{matrix}{f = {- {\frac{\alpha^{- \frac{1}{3}}\sqrt{1 - \alpha^{2}}}{\cos^{- 1}\alpha}.}}} & (12)\end{matrix}$

The projected syncell is also different for Stokes and nonlinearregimes:

$\begin{matrix}{{A_{p} = \left( \frac{3\alpha}{2} \right)^{{- 2}\text{/}3}},} & (13) \\{A_{p} = {\frac{1}{3}\left( {\frac{8\alpha}{\pi} + 1} \right){\left( \frac{3\alpha}{2} \right)^{{- 2}\text{/}3}.}}} & (14)\end{matrix}$

Surface area:

$\begin{matrix}{A_{surf} = {\frac{{2\alpha} + 1}{\left( {18\alpha^{2}} \right)^{1\text{/}3}}.}} & (15)\end{matrix}$

Shape factor:

C _(shape)=1+1.5(A _(surf)−1)^(1/2)+6.7(A _(surf)−1).  (16)

Next, a corrected Reynolds number and a corrected drag coefficient are:

$\begin{matrix}{{{Re}^{*} = \frac{C_{shape}{Re}}{f}},} & (17) \\{C_{d}^{*} = {{\frac{24}{Re}\left( {1 + {0.15{Re}^{*^{0.687}}}} \right)} + {\frac{0.42}{1 + \frac{42500}{{Re}^{*^{1.16}}}}.}}} & (18)\end{matrix}$

The drag coefficient is given by the product of the corrected dragcoefficient and the shape factor: C_(d)=C_(d)*C_(shape).

Relaxation Time.

The drag coefficient for the relaxation time calculations isapproximated using the following empirical formula:

$\begin{matrix}{{C_{d} = \left( {\left( \frac{a}{Re} \right)^{c} + b^{c}} \right)^{1\text{/}c}},} & (19)\end{matrix}$

with constants a=24, b=0.32 and c=0.52, where Re stands for the Reynoldsnumber:

$\begin{matrix}{{{Re} = \frac{\rho_{air}{Dv}}{\eta_{air}}},} & (20)\end{matrix}$

with η_(air) being the dynamic air viscosity.

Cooling Time.

The droplet energy balance is:

P _(evap) =P _(ambient) +P _(cooling).  (21)

The required power to evaporate a volume dV during a small time intervaldt is equal to:

$\begin{matrix}{P_{evap} = {{- \frac{1}{2}}\pi \; h\; \rho_{particle}D^{2}{\frac{dD}{dt}.}}} & (22)\end{matrix}$

The power withdrawn from the syncell for water evaporation is equal to:

$\begin{matrix}{P_{cooling} = {{- \frac{1}{6}}\pi \; c_{p}\rho_{particle}D^{3}{\frac{dT}{dt}.}}} & (23)\end{matrix}$

The heat withdrawn from ambient air (temperature T_(d)) by a drop attemperature T′ can be expressed as:

P _(ambient)=α(T _(d) −T′),  (24)

where α is a heat transfer coefficient that can be determined from thesteady-state evaporation rate. This yields:

$\begin{matrix}{{\frac{dT}{dt} = {{- \frac{3h\; \xi}{c_{p}D^{2}}}\left( {1 + {b\sqrt{Dv}}} \right)\left( {\frac{{dp}_{sat}}{dT} + \gamma} \right)\left( {T^{\prime} - T_{w}} \right)}},} & (25)\end{matrix}$

where:

$\begin{matrix}{{\xi = \frac{4M_{L}D_{vapor}}{\rho_{particle}{RT}}},} & (26) \\{{\frac{{dp}_{sat}}{dT} = {\frac{b_{0}b_{1}\ln \; 10}{\left( {T + b_{1}} \right)^{2}}p_{sat}}},} & (27)\end{matrix}$

with constants b₀=7.5 and b₁=237.3 and p_(sat), the saturated vaporpressure (empirical formula for water):

p _(sat)=610.7 10^(7.5T/(T+237.3)).  (28)

and T_(w) is the wet bulb temperature that can be related to relativehumidity (RH) by the following empirical formula (again for water):

T _(w) =T−((a ₀ +a ₁ T)+(b ₀ +b ₁ T)RH+(c ₀ +c ₁ T)RH ²),  (29)

with constants: a₀=5.11, a₁=0.43 K⁻¹, b₀=−0.047, b₁=−0.0059 K⁻¹,c₀=−4×10⁻⁵ and c₁=1.66×10⁻⁵K⁻¹.

Lifetime.

For lifetime calculations, the average diffusion coefficient for vapormolecules in the saturated film around the drop can be calculated usingthe empirical formula derived for water:

D _(vapor)=21.2*10⁻⁶*(1+0.0071(T−273)).  (30)

Schmidt's number is a dimensionless quantity relating the viscoustransport of a material to its diffusive transport:

$\begin{matrix}{{Sc} = {\frac{\eta_{air}}{\rho_{air}D_{vapor}}.}} & (31)\end{matrix}$

This yields the following formula:

$\begin{matrix}{{\frac{dD}{dt} = {{- \frac{a}{D}}\left( {1 + {b\sqrt{Dv}}} \right)}},} & (32)\end{matrix}$

where a and b are constants depending only on ambient conditions andliquid properties:

$\begin{matrix}{{a = {\frac{4\gamma \; M_{L}D_{vapor}}{\rho_{particle}{RT}}\Delta \; T}},} & (33) \\{b = {0.276{\left( \frac{\rho_{air}}{\eta_{air}D_{vapor}^{2}} \right)^{1\text{/}6}.}}} & (34)\end{matrix}$

Solving this yields:

$\begin{matrix}{{t_{life} = {\frac{2}{q_{0}q_{1}^{2}\Delta \; T}\left( {{q_{1}D_{0}} - {\ln \left( {1 + {q_{1}D_{0}}} \right)}} \right)}},} & (35)\end{matrix}$

where

$\begin{matrix}{{q_{0} = {\frac{2a}{\Delta \; T}\left( {1 + {bs}_{0}} \right)}},} & (36) \\{{q_{1} = \frac{{br}_{0}}{1 + {bs}_{0}}},} & (37)\end{matrix}$

with r₀≈64.65 s^(−0.5) and s₀≈−1.117×10⁻³ m s^(−0.5).

4. MoS₂/TEA Binding Analysis

The reaction between MoS₂ and TEA can be summarized as follows:

$\begin{matrix}{{{{MoS}_{2} + {{TEA}\begin{matrix}\overset{kf}{\rightarrow} \\\underset{kb}{\leftarrow}\end{matrix}{MoS}_{2}\text{/}{TEA}}}\underset{ki}{\rightarrow}{{MoS}_{2} \sim {TEA}}},} & (38)\end{matrix}$

introducing the binding constant k_(ƒ), the association constant k_(b),and the irreversible constant k_(i).

Rate Equations:

$\begin{matrix}{{\frac{{dMoS}_{2}}{dt} = {{{- k_{f}} \cdot {MoS}_{2} \cdot {TEA}} + {{k_{b} \cdot {MoS}_{2}}\text{/}{TEA}}}},} & (39) \\{\frac{{dMoS}_{2}\text{/}{TEA}}{dt} = {{k_{f} \cdot {MoS}_{2} \cdot {TEA}} - {{\left( {k_{b} + k_{i}} \right) \cdot {MoS}_{2}}\text{/}{TEA}}}} & (40)\end{matrix}$

To extract these binding constants, MoS₂ resistance changes previouslymeasured are fitted by Perkins et al. (FIGS. 82A-82B). See, Perkins, F.K., et al., Chemical Vapor Sensing with Monolayer MoS2. Nano Letters,2013. 13(2): p. 668-673, which is incorporated by reference in itsentirety. The initial slope of TEA exposure to MoS₂ was used to extractk_(ƒ); k_(b) was extracted from MoS₂ post-exposure response, whilek_(i)—from the difference between the initial and final MoS₂resistances.

5. State Machine Operation: Power Balance

A successful state machine should not change its state when there is nochemical, even under light illumination. Therefore, the followingcriteria should be met:

$\begin{matrix}{{V_{th} > \frac{ɛ\mspace{14mu} R_{m}^{OFF}}{R_{ph} + R_{m}^{OFF} + R_{ch}^{in}}},} & (41)\end{matrix}$

which sets the boundary for the initial chemiresistance:

$\begin{matrix}{{R_{ch}^{in} > {{R_{m}^{OFF}\left( {\frac{ɛ}{V_{th}} - 1} \right)} - R_{ph}}},} & (42)\end{matrix}$

In this case R_(m) ^(OFF)>>R_(ph) and ε/V_(th)≈2, transforming Eq. (42)into R_(ch) ^(in)>R_(m) ^(OFF). The larger the value of R_(m) ^(OFF),the stronger criteria Eq. (42) becomes.

After reaction with an analyte, chemiresistor decreases its resistanceto R_(ch) ^(ƒ). This allows the voltage across the memristor to reachV_(th), changing its resistance:

$\begin{matrix}{{V_{th} = \frac{ɛ\mspace{14mu} R_{m}^{ON}}{R_{ph} + R_{m}^{ON} + R_{ch}^{f}}},} & (43) \\{R_{m}^{ON} = {\frac{R_{ch}^{f} + R_{ph}}{\frac{ɛ}{V_{th}} - 1}.}} & (44)\end{matrix}$

Estimating Mechanical Forces on CSM During Aerosolization

After liftoff and aerosolization, CSMs can occasionally be bent becauseof the following reasons: (1) turbulent forces during propulsion, (2)collision during landing, or (3) capillary forces during drying (FIGS.75A-75B). The first two factors are similar in a way that they arecaused by rotating dynamics of CSM that is caused by external turbulentforces. Hence, rotational force F_(r), associated with these twoeffects, can be estimated as:

F _(r) ≈mβR,  (45)

where m is CSM mass and β CSM rotational acceleration. Duringpropulsion, CSM experience turbulent flow, meaning that β can beapproximated as

${\beta = {\frac{d\; \omega}{dt} \approx {\frac{1}{2R}\frac{dv}{dt}}}},$

where ω is CSM angular frequency. Taking the nebulizer tube length to be2 cm long, CSM acceleration is estimated as 10³ m/s² and F_(r)=10⁻⁸ N.Capillary forces F_(c) during drying can be calculated as:

F _(c) =σl,  (46)

where σ is water surface tension and l is water perimeter length overwhich CSM bending occurs. Taking σ=0.1 N/m and l=10⁻⁴ m, F_(c)=10⁻⁵ N.

The bending force (F_(b)) for CSM is calculated as:

$\begin{matrix}{{F_{b} = \frac{4{wh}^{3}{dE}}{L^{3}}},} & (47)\end{matrix}$

where w is the CSM width (50 μm), h CSM thickness (1 μm), d bendingdisplacement, E SU-8 Young's modulus (2·10⁹ Pa), and L bending length(50 μm). For minimal displacement of d=1 μm, F_(b)˜10⁻⁶ N. These forcesmay fluctuate a lot due to nonlinear effects and CSM aggregation,however, capillary forces appear to be the most probable reason for CSMdeflection, which is visible in FIGS. 75A-75B, where most CSMs havetheir edges folded. Water droplets of this size dry within 25-160 sec.This indicates that the droplets do not dry throughout their flight; thepresence of a water envelope possibly enhances CSM stability duringlanding and further minimizes the effects of turbulent forces.Strain Guided Fracture Propagation with Stochastic Seed Crack Formation

a. An Existing Model

There is an existing model on soft material fracturing within a strainfield induced by curvature. See Mitchell N P, Koning V, Vitelli V,Irvine W T M. Fracture in sheets draped on curved surfaces. Nat. Mater.2017, 16(1): 89-93, which is incorporated by reference in its entirety.Conforming materials to rigid substrates with Gaussiancurvature—positive for spheres and negative for saddles—has proven aversatile tool to guide the self-assembly of defects such as scars,pleats, folds, blisters, and liquid crystal ripples. It has been shownthat curvature can likewise be used to control material failure andguide the paths of cracks. A simple analytical model has been proposedto capture crack behavior at the onset of propagation, while atwo-dimensional phase-field model with an added curvature termsuccessfully captures the crack's path. Because the curvature-inducedstresses are independent of material parameters for isotropic brittlemedia, these results apply across scales, particularly on the nanometerscale for the generation of microparticles reported thereof.

b. Crack Response to Curvature Stresses and Formulation in Terms ofCurvature Potential

Consider the stresses induced by curvature and their interaction withthe crack tip in a flat sheet. Stresses generated in the bulk of amaterial become concentrated near a crack tip. In turn, a crack extendswhen the intensity of stress concentration exceeds a material-dependent,critical value. Expressed mathematically, in the local coordinates ofthe crack tip (r, θ), the stress in the vicinity of the tip takes theform

$\begin{matrix}{\sigma_{ij} = {{\frac{K_{I}}{\sqrt{2\pi \; r}}{f_{ij}^{I}(\theta)}} + {\frac{K_{II}}{\sqrt{2\pi \; r}}{f_{ij}^{II}(\theta)}}}} & (48)\end{matrix}$

where ƒ_(ij) ^(I,II) are universal angular functions. The factors K_(I)and K_(II) measure the intensity of tensile and shear stressconcentration at the crack tip, respectively, and are known as stressintensity factors. Thus, the Griffith length, a_(c), is the length ofthe crack at which the intensity of stress concentration reaches thecritical value, K_(c). In curved plates or sheets, the near-tip stressfields display the same singular behavior as in Eq. (48), but the valuesof the stress intensity factors are governed by curvature.

Curving a flat sheet involves locally stretching and compressing thematerial by certain amounts at each point. According to the rules ofdifferential geometry, this stretching factor, controlled by the fieldΦ(ρ), is determined by an equation identical to the Poisson equation ofelectrostatics, with the Gaussian curvature, G(ρ), playing the role of acontinuous charge distribution

∇²Φ(ρ)=−G(ρ)  (49)

As the sheet equilibrates, its elasticity tends to oppose thismechanical constraint, giving rise to stress. The isotropic stress fromcurvature is then related to the potential via

σ_(kk) ^(G) =EΦ  (50)

where E is the Young's modulus, and the stress components are determinedby integrals of the curvature potential. It has been reported previouslythat positive (negative) curvature promotes local stretching(compression) of an elastic sheet, leading to the enhancement(suppression) of crack initiation. Variations in the potential Φ(ρ)steer the crack path, with the form determined from the curvaturedistribution.

Curvature not only governs the critical length for fracture initiation,but also the direction of a crack's propagation. For cracks inclinedwith respect to the bump, the cracks change direction as they begin topropagate, kinking at the onset of crack growth and curving around thebump. Cracks kink and curve towards the azimuthal direction because adecaying curvature potential, Φ(ρ), creates a local stress asymmetry. Asa result, the crack relieves more elastic energy by deflecting towardsthe azimuthal direction. Analytical prediction of the kink angle, θ_(k),has previously been made by selecting the direction of maximum hoopstress asymptotically near the crack tip.

Given knowledge of the stress field of an uncracked sheet on a curvedsurface, the stress intensity factors (K_(I), K_(II)) for a crack onthat curved surface has been calculated previously. See Zhang P, Ma L,Fan F, Zeng Z, Peng C, Loya P E, et al. Fracture toughness of graphene.Nat. Commun. 2014, 5: 3782, which is incorporated by reference in itsentirety. These quantities measure the intensity of tensile and shearstress concentration at the crack tip. The stress intensity factors foreach seed crack position and orientation follow from integrating theinfinite-plane Westergaard solution over the crack length

$\begin{matrix}{{K_{I,{II}} = {\frac{1}{\sqrt{\pi \; a}}{\int\limits_{- a}^{a}{\sqrt{\frac{a + \xi}{a - \xi}}\text{?}}}}}{\text{?}\text{indicates text missing or illegible when filed}}} & (51)\end{matrix}$

where

and

are the tensile and shear stresses, respectively, in the crack's localx-y coordinate system. The tilde distinguishes

from σ_(ij)(ρ,ϕ), which is a function of the material coordinate systemrather than the crack coordinate system and is therefore a differentfunction of its arguments, despite being the same physical quantity.Here a is the crack length, and by selecting the direction of maximumhoop stress (

) at the crack tip as the direction of crack propagation, the kink angleat the onset of propagation takes the form

$\begin{matrix}{\theta_{k} = {2{\arctan\left( \frac{2\eta}{1 + \sqrt{1 + {8\eta^{2}}}} \right)}}} & (52)\end{matrix}$

where η=K_(II)/K_(I) and if a crack whose length is relatively smallcompared to the length scale over which the stress fields vary, that is,

${a{\frac{\partial}{\text{?}{\partial x}}}{\square\text{?}}},{\text{?}\text{indicates text missing or illegible when filed}}$

the expression for η simplifies, because

K _(I)=√{square root over(πa)}(σ_(ρρ)(ρ*)sin²(β)+σ_(ϕϕ)(ρ*)cos²(β)  (53)

K _(II)=√{square root over(πa)}{σ_(ϕϕ)(ρ*)−σ_(ρρ)(ρ*)}sin(β)cos(β)  (54)

where the inclination angle β is the angle of the seed crack withrespect to the radial direction. Since K_(II) vanishes for radial andazimuthal cracks (β=0, π/2), these cracks do not kink, while forintermediate values of β, that is, for β mod

${\left( \frac{\pi}{2} \right) \neq 0},$

the shear stress on the crack, measured by K_(II), will be nonzero.Therefore, if the crack grows, it will kink at the onset of propagation.

For azimuthal seed cracks (β=π/2), there is no kink because the loadingis mode I (tensile) for small seed cracks, but as the crack grows, theasymmetric stresses from curvature direct the crack in a continuous arc.The Griffith length (a_(c)) of a crack is the length at which the energyreleased by extending the crack exceeds the fracture energy. Thiscorresponds to the condition that the intensity of stress concentrationin some direction θ exceeds the critical stress intensity factor K_(c).For a crack which is small compared to the scale of stress variations,again centered at ρ=ρ* with inclination angle β, the Griffith length canbe expressed as

$\begin{matrix}{a_{c} \approx \frac{K_{c}^{2}}{\pi \left\{ {{{\sigma_{yy}\left( \rho^{*} \right)}{f_{\theta\theta}^{I}\left( \overset{\_}{\theta} \right)}} + {{\sigma_{xy}\left( \rho^{*} \right)}{f_{\theta\theta}^{II}\left( \overset{\_}{\theta} \right)}}} \right\}^{2}}} & (55)\end{matrix}$

where θ=−θ_(k) is the direction of maximum hoop stress, and ƒ_(ij)^(I,II) are universal angular functions, and the stresses are

σ_(yy)(ρ*)=σ_(ρρ)(ρ*)sin²(β)+σ_(ϕϕ)(ρ*)cos²(β)  (56)

σ_(xy)(ρ*)={σ_(ϕϕ)(ρ*)−σ_(ρρ)(ρ*)}sin(β)cos(β)  (57)

If small cracks were considered, expressions for the kink angle andGriffith length are in terms of the curvature potential Φ(ρ). For anyrotationally symmetric curvature distribution G(ρ), it has been shownthat the ratio of the stress intensity factors of a small crack centeredat ρ* is

$\begin{matrix}{\eta = \frac{\left( {\Phi - \Omega} \right){\sin \left( {2\beta} \right)}}{\Phi + {\left( {\Phi - \Omega} \right){\cos \left( {2\beta} \right)}}}} & (58)\end{matrix}$

where

$\begin{matrix}{{\Omega \left( \rho^{*} \right)} \equiv {\frac{2}{\rho^{*2}}{\int\limits_{0}^{\rho^{*}}{\rho^{\prime}{\Phi \left( \rho^{\prime} \right)}d\; \rho^{\prime}}}}} & (59)\end{matrix}$

is the average value of the curvature potential in the region enclosedby the circle of radius ρ*. Thus, the quantity Φ−Ω appearing in Eq. (58)is the difference between the local value of the potential Φ(ρ*) and thevalue of the potential averaged from the center to the location of thecrack, and this quantity can be readily identified as the local stressasymmetry.

For the crack to propagate, the tractions along the crack faces must bepositive. Therefore, the sign of this stress asymmetry determineswhether the crack kinks towards the radial or azimuthal direction. For acrack in a potential “well” (where Φ increases with radial distance),the crack kinks toward the radial direction (with respect to the centerof the well). For a crack in a potential “dome” or “peak” (where Φdecreases with radial distance), the crack kinks toward the azimuthaldirection. Note this in turn establishes the guiding principle thatdirects crack propagation along “maximum hoop strain” that has beenexploited to great effect in this work.

The Griffith length for the small crack can likewise be computed from asymmetric curvature potential, Φ(ρ), via

$\begin{matrix}{a_{c} = \frac{4K_{c}^{2}}{\pi \; E^{2}\left\{ {{2\Phi \; {F\left( {\overset{\_}{\theta},\beta} \right)}{\cos (\beta)}} - {\Omega \; {F\left( {\overset{\_}{\theta},{2\beta}} \right)}}} \right\}^{2}}} & (60)\end{matrix}$

-   -   where

F(θ,β)=ƒ_(θθ) ^(I)(θ)cos(β)+ƒ_(θθ) ^(II)(θ)sin(β)  (61)

Note that the curvature potential measures the local isotropiccompression

$\begin{matrix}{{{\theta \left( \overset{\rightarrow}{x} \right)} = \frac{\text{?}}{E}}{\text{?}\text{indicates text missing or illegible when filed}}} & (62)\end{matrix}$

This implies that crack growth tends to be suppressed in regions whereΦ<0 and stimulated where Φ>0. A local stress asymmetry, however, canplay an important role in attenuating this generalization. A curvaturepotential which increases with radial distance (a potential “well”)preferentially stimulates the growth of cracks which are oriented alongthe radial direction, so that the Griffith length of a radial crack in apotential well is smaller than that of an azimuthal crack centered thesame distance ρ* from the minimum of Φ. Conversely, potentials, whichdecrease with distance from the center preferentially, stimulate thegrowth of cracks oriented along the azimuthal direction.

c. Estimation of the Griffith Length for Free-Standing Graphene

The minimum seed crack needed for run-away fracture propagation onfreestanding graphene is estimated using Eq. (60) and (61). First, it isneeded to figure out what function form each term takes on. In terms ofthe universal angular functions, coordinate transformation is performed(from local Cartesian to global Polar) for mode I as such

$\begin{matrix}{{f_{xx}^{I}\left( \overset{\_}{\theta} \right)} = {{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}\left\{ {1 - {{\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\sin \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} \right\}}} & (63) \\{{f_{xy}^{I}\left( \overset{\_}{\theta} \right)} = {{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\cos \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} & (64) \\{{f_{yy}^{I}\left( \overset{\_}{\theta} \right)} = {{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}\left\{ {1 + {{\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\sin \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} \right\}}} & (65)\end{matrix}$Recall that

ƒ_(θθ) ^(I) ={right arrow over (e)} _(θ) ·

·{right arrow over (e)} _(θ)  (66)

and

{right arrow over (e)} _(θ)=−sin(θ){right arrow over (e)}_(x)+cos(θ){right arrow over (e)} _(y)  (67)

where a universal function angular function tensor

was defined with the following form

$\begin{matrix}{{{\underset{.\mspace{14mu}.}{f}}^{I} = \begin{bmatrix}f_{xx}^{I} & f_{xy}^{I} \\\text{?} & f_{yx}^{I}\end{bmatrix}}{\text{?}\text{indicates text missing or illegible when filed}}} & (68)\end{matrix}$

If

is a symmetric tensor (i e. ƒ_(ij) ^(I)=ƒ_(ji) ^(I)) it follows that

ƒ_(θθ) ^(I)(θ)=sin²(θ)ƒ_(xx) ^(I)(θ)−2 sin(θ)cos(θ)ƒ_(xy)^(I)(θ)+cos²(θ)ƒ_(yy) ^(I)(θ)  (69)

Similarly, mode II is calculated,

ƒ_(θθ) ^(II)(θ)=sin²(θ)ƒ_(xx) ^(II)(θ)−2 sin(θ)cos(θ)ƒ_(xy)^(II)(θ)+cos²(θ)ƒ_(yy) ^(II)(θ)  (70)

given that

$\begin{matrix}{{f_{xx}^{II}\left( \overset{\_}{\theta} \right)} = {{- {\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}}\left\{ {2 + {{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\cos \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} \right\}}} & (71) \\{{f_{xy}^{II}\left( \overset{\_}{\theta} \right)} = {{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}\left\{ {1 - {{\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\sin \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} \right\}}} & (72) \\{{f_{yy}^{II}\left( \overset{\_}{\theta} \right)} = {{\sin \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\cos \left( {\frac{1}{2}\overset{\_}{\theta}} \right)}{\cos \left( {\frac{3}{2}\overset{\_}{\theta}} \right)}}} & (73)\end{matrix}$

In terms of the other parameter values, the critical stress intensityfactor for monolayer graphene, K_(c), has recently been experimentallymeasured to be 4.0±0.6 MPa·m^(1/2) (see Zhang P, Ma L, Fan F, Zeng Z,Peng C, Loya P E, et al. Fracture toughness of graphene. Nat. Commun.2014, 5: 3782, which is incorporated by reference in its entirety) andthe Young's modulus of graphene, E, is approximately 1 TPa (see Lee G-H,Cooper R C, An S J, Lee S, van der Zande A, Petrone N, et al.High-Strength Chemical-Vapor-Deposited Graphene and Grain Boundaries.Science 2013, 340(6136): 1073-1076, which is incorporated by referencein its entirety); as for Φ, it is just the curvature potential (orlattice strain), which according to the simulation in the abovesections, is estimated to be around 1% at the point of maximum strain.With these, all possible values of β's can be scanned over and θ's andplot the Griffith lengths in units of meters. In this phase space, thereare large areas where the Griffith lengths are as low as 10 nm, whichwill automatically perforate under this strain, given the random seedcracks/defects present in monolayer graphene grown under laboratory CVDconditions (FIG. 87).

e. Kinetic Monte-Carlo Simulation of Crack Propagation

A kinetic Monte-Carlo model (rejection KMC method) is created tosimulate the stochastic crack initiation and propagation. To monitor thefracture path at the micrometer level, 2D square lattice is used tocapture the birds-eye geometry of the graphene-polystyrene-grapheneink-jet printed array. Crack initiation is assigned randomly with agiven probability over the entire graphene lattice at each iterationstep. Transition rates for continued propagation at each of the fourpossible directions are then calculated and executed accordingly. Uponthe creation of the 2D lattice, the key iteration steps can besummarized generically as following:

1. Set the time to t=0.

2. Choose an initial state k.

3. Get the number N_(k) of all possible transition rates, from state kinto state i.

4. Find the propagation event to carry out i by uniformly sampling fromthe N_(k) transitions above.

5. Accept the event with probability ƒ_(ki)=r_(ki)/r₀, where r₀ is asuitable upper bound for r_(ki).

6. If accepted, update the current state from k to i.

7. Get a new uniform random number u′ from 0 to 1. 8. Update the timewith t=t+Δt, where Δt=(N_(k)r₀)⁻¹ln(l/u′).

9. Return to step 3.

Three example simulation results are shown (FIG. 88). The propagationevents are captured and the polystyrene microspots serve to attractpropagating cracks as well as directing the cracks around theirperimeters to guide and ensure a perfect autoperforation process.

If the crack formation can be zoomed in and compared with microscopyresults, the simulation seems to corroborate well with experimentalobservations (FIG. 89), further establishing the validity of the modelbased approach.

Other embodiments are within the scope of the following claims.

1. An particle comprising: a first sheet comprising a layer including afirst material, wherein the first sheet includes a first outer surfaceand a first inner surface; and a second sheet comprising a layerincluding a second material, wherein the second sheet includes a secondouter surface and a second inner surface, wherein the first sheet andthe second sheet form a space, the space is encapsulated by the firstsheet and the second sheet.
 2. The particle of claim 1, wherein thefirst sheet further comprises a second layer including the firstmaterial.
 3. The particle of claim 1, wherein the second sheet furthercomprises a second layer including the second material.
 4. The particleof claim 1, wherein the first material is graphene, molybdenumdisulfide, hexagonal boron nitride (hBN), molybdenum diselenide,tungsten disulfide, tungsten diselenide, rhenium diselenide, rheniumdisulfide, black phosphorus, platinum diselenide, tin sulfide, or tinselenide.
 5. The particle of claim 1, wherein the second material isgraphene, molybdenum disulfide, hexagonal boron nitride (hBN),molybdenum diselenide, tungsten disulfide, tungsten diselenide, rheniumdiselenide, rhenium disulfide, black phosphorus, platinum diselenide,tin sulfide, or tin selenide.
 6. The particle of claim 1, wherein thefirst outer surface is functionalized.
 7. The particle of claim 6,wherein the first outer surface is covalently functionalized.
 8. Theparticle of claim 6, wherein the first outer surface is noncovalentlyfunctionalized.
 9. The particle of claim 7, wherein the first outersurface is functionalized via π-π stacking.
 10. The particle of claim 1,wherein the first inner surface is functionalized.
 11. The particle ofclaim 10, wherein the first outer surface is covalently functionalized.12. The particle of claim 10, wherein the first outer surface isnoncovalently functionalized.
 13. The particle of claim 12, wherein thefirst outer surface is functionalized via π-π stacking.
 14. The particleof claim 1, wherein the second outer surface is functionalized.
 15. Theparticle of claim 14, wherein the first outer surface is covalentlyfunctionalized.
 16. The particle of claim 14, wherein the first outersurface is noncovalently functionalized.
 17. The particle of claim 16,wherein the first outer surface is functionalized via π-π stacking. 18.The particle of claim 1, wherein the second inner surface isfunctionalized.
 19. The particle of claim 18, wherein the first outersurface is covalently functionalized.
 20. The particle of claim 18,wherein the first outer surface is noncovalently functionalized.
 21. Theparticle of claim 20, wherein the first outer surface is functionalizedvia π-π stacking.
 22. The particle of claim 1, wherein the first sheetincludes a plurality of nanopores.
 23. The particle of claim 1, whereinthe second sheet includes a plurality of nanopores.
 24. The particle ofclaim 1, wherein the space includes a composition.
 25. The particle ofclaim 24, wherein the composition includes electronics.
 26. The particleof claim 24, wherein the composition includes liquid.
 27. The particleof claim 24, wherein the composition includes gel.
 28. The particle ofclaim 24, wherein the composition includes a nanoparticle.
 29. A methodof making an particle comprising: preparing a first sheet including afirst substrate and a first layer comprising a first material on a firstsubstrate, wherein the first sheet includes a first outer surface and afirst inner surface; depositing a composition; preparing a second sheetincluding a second substrate and a second sheet comprising a secondmaterial on the second substrate, wherein the second sheet includes asecond outer surface and a first inner surface; annealing the firstsheet and the second sheet; and autoperforating the first sheet and thesecond sheet. 30.-41. (canceled)
 42. A method of detecting an analytecomprising: applying the particle of claim 1, wherein the space includesa sensor; and detecting the analyte with the sensor. 43.-44. (canceled)45. A device comprising: a sheet including a substrate material; a powersource on the substrate; a switch on the substrate; and a memory elementon the substrate. 46.-61. (canceled)
 62. A method of making a devicecomprising: preparing a substrate; depositing a first monolayer ofincluding MoS₂ on the substrate; depositing a second monolayer includingWSe₂ at least partially in contact with the monolayer including MoS₂;depositing a gold electrode on a portion of the first monolayer;depositing a gold electrode on a portion of the second monolayer;depositing a material including MoS₂ in contact with the gold electrodeon the first monolayer and in contact with the second monolayer;depositing a silver electrode in contact with the gold electrode; anddepositing a silver electrode in contact with the material includingMoS₂. 63.-65. (canceled)